Adding upstream version 1:10.5.12.upstream/1%10.5.12upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4811 insertions, 0 deletions

diff --git a/storage/innobase/ibuf/ibuf0ibuf.cc b/storage/innobase/ibuf/ibuf0ibuf.cc
new file mode 100644
index 00000000..9288a496
--- /dev/null
+++ b/storage/innobase/ibuf/ibuf0ibuf.cc
@@ -0,0 +1,4811 @@
+/*****************************************************************************
+
+Copyright (c) 1997, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2016, 2021, MariaDB Corporation.
+
+This program is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free Software
+Foundation; version 2 of the License.
+
+This program is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
+
+*****************************************************************************/
+
+/**************************************************//**
+@file ibuf/ibuf0ibuf.cc
+Insert buffer
+
+Created 7/19/1997 Heikki Tuuri
+*******************************************************/
+
+#include "ibuf0ibuf.h"
+#include "sync0sync.h"
+#include "btr0sea.h"
+
+/** Number of bits describing a single page */
+#define IBUF_BITS_PER_PAGE	4
+/** The start address for an insert buffer bitmap page bitmap */
+#define IBUF_BITMAP		PAGE_DATA
+
+#include "buf0buf.h"
+#include "buf0rea.h"
+#include "fsp0fsp.h"
+#include "trx0sys.h"
+#include "fil0fil.h"
+#include "rem0rec.h"
+#include "btr0cur.h"
+#include "btr0pcur.h"
+#include "btr0btr.h"
+#include "row0upd.h"
+#include "dict0boot.h"
+#include "fut0lst.h"
+#include "lock0lock.h"
+#include "log0recv.h"
+#include "que0que.h"
+#include "srv0start.h" /* srv_shutdown_state */
+#include "rem0cmp.h"
+
+/*	STRUCTURE OF AN INSERT BUFFER RECORD
+
+In versions < 4.1.x:
+
+1. The first field is the page number.
+2. The second field is an array which stores type info for each subsequent
+   field. We store the information which affects the ordering of records, and
+   also the physical storage size of an SQL NULL value. E.g., for CHAR(10) it
+   is 10 bytes.
+3. Next we have the fields of the actual index record.
+
+In versions >= 4.1.x:
+
+Note that contary to what we planned in the 1990's, there will only be one
+insert buffer tree, and that is in the system tablespace of InnoDB.
+
+1. The first field is the space id.
+2. The second field is a one-byte marker (0) which differentiates records from
+   the < 4.1.x storage format.
+3. The third field is the page number.
+4. The fourth field contains the type info, where we have also added 2 bytes to
+   store the charset. In the compressed table format of 5.0.x we must add more
+   information here so that we can build a dummy 'index' struct which 5.0.x
+   can use in the binary search on the index page in the ibuf merge phase.
+5. The rest of the fields contain the fields of the actual index record.
+
+In versions >= 5.0.3:
+
+The first byte of the fourth field is an additional marker (0) if the record
+is in the compact format.  The presence of this marker can be detected by
+looking at the length of the field modulo DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE.
+
+The high-order bit of the character set field in the type info is the
+"nullable" flag for the field.
+
+In versions >= 5.5:
+
+The optional marker byte at the start of the fourth field is replaced by
+mandatory 3 fields, totaling 4 bytes:
+
+ 1. 2 bytes: Counter field, used to sort records within a (space id, page
+    no) in the order they were added. This is needed so that for example the
+    sequence of operations "INSERT x, DEL MARK x, INSERT x" is handled
+    correctly.
+
+ 2. 1 byte: Operation type (see ibuf_op_t).
+
+ 3. 1 byte: Flags. Currently only one flag exists, IBUF_REC_COMPACT.
+
+To ensure older records, which do not have counters to enforce correct
+sorting, are merged before any new records, ibuf_insert checks if we're
+trying to insert to a position that contains old-style records, and if so,
+refuses the insert. Thus, ibuf pages are gradually converted to the new
+format as their corresponding buffer pool pages are read into memory.
+*/
+
+
+/*	PREVENTING DEADLOCKS IN THE INSERT BUFFER SYSTEM
+
+If an OS thread performs any operation that brings in disk pages from
+non-system tablespaces into the buffer pool, or creates such a page there,
+then the operation may have as a side effect an insert buffer index tree
+compression. Thus, the tree latch of the insert buffer tree may be acquired
+in the x-mode, and also the file space latch of the system tablespace may
+be acquired in the x-mode.
+
+Also, an insert to an index in a non-system tablespace can have the same
+effect. How do we know this cannot lead to a deadlock of OS threads? There
+is a problem with the i\o-handler threads: they break the latching order
+because they own x-latches to pages which are on a lower level than the
+insert buffer tree latch, its page latches, and the tablespace latch an
+insert buffer operation can reserve.
+
+The solution is the following: Let all the tree and page latches connected
+with the insert buffer be later in the latching order than the fsp latch and
+fsp page latches.
+
+Insert buffer pages must be such that the insert buffer is never invoked
+when these pages are accessed as this would result in a recursion violating
+the latching order. We let a special i/o-handler thread take care of i/o to
+the insert buffer pages and the ibuf bitmap pages, as well as the fsp bitmap
+pages and the first inode page, which contains the inode of the ibuf tree: let
+us call all these ibuf pages. To prevent deadlocks, we do not let a read-ahead
+access both non-ibuf and ibuf pages.
+
+Then an i/o-handler for the insert buffer never needs to access recursively the
+insert buffer tree and thus obeys the latching order. On the other hand, other
+i/o-handlers for other tablespaces may require access to the insert buffer,
+but because all kinds of latches they need to access there are later in the
+latching order, no violation of the latching order occurs in this case,
+either.
+
+A problem is how to grow and contract an insert buffer tree. As it is later
+in the latching order than the fsp management, we have to reserve the fsp
+latch first, before adding or removing pages from the insert buffer tree.
+We let the insert buffer tree have its own file space management: a free
+list of pages linked to the tree root. To prevent recursive using of the
+insert buffer when adding pages to the tree, we must first load these pages
+to memory, obtaining a latch on them, and only after that add them to the
+free list of the insert buffer tree. More difficult is removing of pages
+from the free list. If there is an excess of pages in the free list of the
+ibuf tree, they might be needed if some thread reserves the fsp latch,
+intending to allocate more file space. So we do the following: if a thread
+reserves the fsp latch, we check the writer count field of the latch. If
+this field has value 1, it means that the thread did not own the latch
+before entering the fsp system, and the mtr of the thread contains no
+modifications to the fsp pages. Now we are free to reserve the ibuf latch,
+and check if there is an excess of pages in the free list. We can then, in a
+separate mini-transaction, take them out of the free list and free them to
+the fsp system.
+
+To avoid deadlocks in the ibuf system, we divide file pages into three levels:
+
+(1) non-ibuf pages,
+(2) ibuf tree pages and the pages in the ibuf tree free list, and
+(3) ibuf bitmap pages.
+
+No OS thread is allowed to access higher level pages if it has latches to
+lower level pages; even if the thread owns a B-tree latch it must not access
+the B-tree non-leaf pages if it has latches on lower level pages. Read-ahead
+is only allowed for level 1 and 2 pages. Dedicated i/o-handler threads handle
+exclusively level 1 i/o. A dedicated i/o handler thread handles exclusively
+level 2 i/o. However, if an OS thread does the i/o handling for itself, i.e.,
+it uses synchronous aio, it can access any pages, as long as it obeys the
+access order rules. */
+
+/** Operations that can currently be buffered. */
+ulong	innodb_change_buffering;
+
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+/** Dump the change buffer at startup */
+my_bool	ibuf_dump;
+/** Flag to control insert buffer debugging. */
+uint	ibuf_debug;
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
+/** The insert buffer control structure */
+ibuf_t	ibuf;
+
+/** @name Offsets to the per-page bits in the insert buffer bitmap */
+/* @{ */
+#define	IBUF_BITMAP_FREE	0	/*!< Bits indicating the
+					amount of free space */
+#define IBUF_BITMAP_BUFFERED	2	/*!< TRUE if there are buffered
+					changes for the page */
+#define IBUF_BITMAP_IBUF	3	/*!< TRUE if page is a part of
+					the ibuf tree, excluding the
+					root page, or is in the free
+					list of the ibuf */
+/* @} */
+
+#define IBUF_REC_FIELD_SPACE	0	/*!< in the pre-4.1 format,
+					the page number. later, the space_id */
+#define IBUF_REC_FIELD_MARKER	1	/*!< starting with 4.1, a marker
+					consisting of 1 byte that is 0 */
+#define IBUF_REC_FIELD_PAGE	2	/*!< starting with 4.1, the
+					page number */
+#define IBUF_REC_FIELD_METADATA	3	/* the metadata field */
+#define IBUF_REC_FIELD_USER	4	/* first user field */
+
+/* Various constants for checking the type of an ibuf record and extracting
+data from it. For details, see the description of the record format at the
+top of this file. */
+
+/** @name Format of the IBUF_REC_FIELD_METADATA of an insert buffer record
+The fourth column in the MySQL 5.5 format contains an operation
+type, counter, and some flags. */
+/* @{ */
+#define IBUF_REC_INFO_SIZE	4	/*!< Combined size of info fields at
+					the beginning of the fourth field */
+
+/* Offsets for the fields at the beginning of the fourth field */
+#define IBUF_REC_OFFSET_COUNTER	0	/*!< Operation counter */
+#define IBUF_REC_OFFSET_TYPE	2	/*!< Type of operation */
+#define IBUF_REC_OFFSET_FLAGS	3	/*!< Additional flags */
+
+/* Record flag masks */
+#define IBUF_REC_COMPACT	0x1	/*!< Set in
+					IBUF_REC_OFFSET_FLAGS if the
+					user index is in COMPACT
+					format or later */
+
+
+/** The mutex used to block pessimistic inserts to ibuf trees */
+static ib_mutex_t	ibuf_pessimistic_insert_mutex;
+
+/** The mutex protecting the insert buffer structs */
+static ib_mutex_t	ibuf_mutex;
+
+/** The mutex protecting the insert buffer bitmaps */
+static ib_mutex_t	ibuf_bitmap_mutex;
+
+/** The area in pages from which contract looks for page numbers for merge */
+const ulint		IBUF_MERGE_AREA = 8;
+
+/** Inside the merge area, pages which have at most 1 per this number less
+buffered entries compared to maximum volume that can buffered for a single
+page are merged along with the page whose buffer became full */
+const ulint		IBUF_MERGE_THRESHOLD = 4;
+
+/** In ibuf_contract at most this number of pages is read to memory in one
+batch, in order to merge the entries for them in the insert buffer */
+const ulint		IBUF_MAX_N_PAGES_MERGED = IBUF_MERGE_AREA;
+
+/** If the combined size of the ibuf trees exceeds ibuf.max_size by
+this many pages, we start to contract it synchronous contract, but do
+not insert */
+const ulint		IBUF_CONTRACT_DO_NOT_INSERT = 10;
+
+/* TODO: how to cope with drop table if there are records in the insert
+buffer for the indexes of the table? Is there actually any problem,
+because ibuf merge is done to a page when it is read in, and it is
+still physically like the index page even if the index would have been
+dropped! So, there seems to be no problem. */
+
+/******************************************************************//**
+Sets the flag in the current mini-transaction record indicating we're
+inside an insert buffer routine. */
+UNIV_INLINE
+void
+ibuf_enter(
+/*=======*/
+	mtr_t*	mtr)	/*!< in/out: mini-transaction */
+{
+	ut_ad(!mtr->is_inside_ibuf());
+	mtr->enter_ibuf();
+}
+
+/******************************************************************//**
+Sets the flag in the current mini-transaction record indicating we're
+exiting an insert buffer routine. */
+UNIV_INLINE
+void
+ibuf_exit(
+/*======*/
+	mtr_t*	mtr)	/*!< in/out: mini-transaction */
+{
+	ut_ad(mtr->is_inside_ibuf());
+	mtr->exit_ibuf();
+}
+
+/**************************************************************//**
+Commits an insert buffer mini-transaction and sets the persistent
+cursor latch mode to BTR_NO_LATCHES, that is, detaches the cursor. */
+UNIV_INLINE
+void
+ibuf_btr_pcur_commit_specify_mtr(
+/*=============================*/
+	btr_pcur_t*	pcur,	/*!< in/out: persistent cursor */
+	mtr_t*		mtr)	/*!< in/out: mini-transaction */
+{
+	ut_d(ibuf_exit(mtr));
+	btr_pcur_commit_specify_mtr(pcur, mtr);
+}
+
+/******************************************************************//**
+Gets the ibuf header page and x-latches it.
+@return insert buffer header page */
+static
+page_t*
+ibuf_header_page_get(
+/*=================*/
+	mtr_t*	mtr)	/*!< in/out: mini-transaction */
+{
+	buf_block_t*	block;
+
+	ut_ad(!ibuf_inside(mtr));
+	page_t* page = NULL;
+
+	block = buf_page_get(
+		page_id_t(IBUF_SPACE_ID, FSP_IBUF_HEADER_PAGE_NO),
+		0, RW_X_LATCH, mtr);
+
+	if (block) {
+		buf_block_dbg_add_level(block, SYNC_IBUF_HEADER);
+		page = buf_block_get_frame(block);
+	}
+
+	return page;
+}
+
+/** Acquire the change buffer root page.
+@param[in,out]  mtr     mini-transaction
+@return change buffer root page, SX-latched */
+static buf_block_t *ibuf_tree_root_get(mtr_t *mtr)
+{
+	buf_block_t*	block;
+
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(mutex_own(&ibuf_mutex));
+
+	mtr_sx_lock_index(ibuf.index, mtr);
+
+	/* only segment list access is exclusive each other */
+	block = buf_page_get(
+		page_id_t(IBUF_SPACE_ID, FSP_IBUF_TREE_ROOT_PAGE_NO),
+		0, RW_SX_LATCH, mtr);
+
+	buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE_NEW);
+
+	ut_ad(page_get_space_id(block->frame) == IBUF_SPACE_ID);
+	ut_ad(page_get_page_no(block->frame) == FSP_IBUF_TREE_ROOT_PAGE_NO);
+	ut_ad(ibuf.empty == page_is_empty(block->frame));
+
+	return block;
+}
+
+/******************************************************************//**
+Closes insert buffer and frees the data structures. */
+void
+ibuf_close(void)
+/*============*/
+{
+	if (!ibuf.index) {
+		return;
+	}
+
+	mutex_free(&ibuf_pessimistic_insert_mutex);
+
+	mutex_free(&ibuf_mutex);
+
+	mutex_free(&ibuf_bitmap_mutex);
+
+	dict_table_t*	ibuf_table = ibuf.index->table;
+	rw_lock_free(&ibuf.index->lock);
+	dict_mem_index_free(ibuf.index);
+	dict_mem_table_free(ibuf_table);
+	ibuf.index = NULL;
+}
+
+/******************************************************************//**
+Updates the size information of the ibuf, assuming the segment size has not
+changed. */
+static
+void
+ibuf_size_update(
+/*=============*/
+	const page_t*	root)	/*!< in: ibuf tree root */
+{
+	ut_ad(mutex_own(&ibuf_mutex));
+
+	ibuf.free_list_len = flst_get_len(root + PAGE_HEADER
+					   + PAGE_BTR_IBUF_FREE_LIST);
+
+	ibuf.height = 1 + btr_page_get_level(root);
+
+	/* the '1 +' is the ibuf header page */
+	ibuf.size = ibuf.seg_size - (1 + ibuf.free_list_len);
+}
+
+/******************************************************************//**
+Creates the insert buffer data structure at a database startup and initializes
+the data structures for the insert buffer.
+@return DB_SUCCESS or failure */
+dberr_t
+ibuf_init_at_db_start(void)
+/*=======================*/
+{
+	page_t*		root;
+	ulint		n_used;
+
+	ut_ad(!ibuf.index);
+	mtr_t mtr;
+	mtr.start();
+	compile_time_assert(IBUF_SPACE_ID == TRX_SYS_SPACE);
+	compile_time_assert(IBUF_SPACE_ID == 0);
+	mtr_x_lock_space(fil_system.sys_space, &mtr);
+	buf_block_t* header_page = buf_page_get(
+		page_id_t(IBUF_SPACE_ID, FSP_IBUF_HEADER_PAGE_NO),
+		0, RW_X_LATCH, &mtr);
+
+	if (!header_page) {
+		mtr.commit();
+		return DB_DECRYPTION_FAILED;
+	}
+
+	/* At startup we intialize ibuf to have a maximum of
+	CHANGE_BUFFER_DEFAULT_SIZE in terms of percentage of the
+	buffer pool size. Once ibuf struct is initialized this
+	value is updated with the user supplied size by calling
+	ibuf_max_size_update(). */
+	ibuf.max_size = ((buf_pool_get_curr_size() >> srv_page_size_shift)
+			  * CHANGE_BUFFER_DEFAULT_SIZE) / 100;
+
+	mutex_create(LATCH_ID_IBUF, &ibuf_mutex);
+
+	mutex_create(LATCH_ID_IBUF_BITMAP, &ibuf_bitmap_mutex);
+
+	mutex_create(LATCH_ID_IBUF_PESSIMISTIC_INSERT,
+		     &ibuf_pessimistic_insert_mutex);
+
+	mutex_enter(&ibuf_mutex);
+
+	fseg_n_reserved_pages(*header_page,
+			      IBUF_HEADER + IBUF_TREE_SEG_HEADER
+			      + header_page->frame, &n_used, &mtr);
+
+	ut_ad(n_used >= 2);
+
+	ibuf.seg_size = n_used;
+
+	{
+		buf_block_t*	block;
+
+		block = buf_page_get(
+			page_id_t(IBUF_SPACE_ID, FSP_IBUF_TREE_ROOT_PAGE_NO),
+			0, RW_X_LATCH, &mtr);
+
+		buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE);
+
+		root = buf_block_get_frame(block);
+	}
+
+	ibuf_size_update(root);
+	mutex_exit(&ibuf_mutex);
+
+	ibuf.empty = page_is_empty(root);
+	mtr.commit();
+
+	ibuf.index = dict_mem_index_create(
+		dict_mem_table_create("innodb_change_buffer",
+				      fil_system.sys_space, 1, 0, 0, 0),
+		"CLUST_IND",
+		DICT_CLUSTERED | DICT_IBUF, 1);
+	ibuf.index->id = DICT_IBUF_ID_MIN + IBUF_SPACE_ID;
+	ibuf.index->n_uniq = REC_MAX_N_FIELDS;
+	rw_lock_create(index_tree_rw_lock_key, &ibuf.index->lock,
+		       SYNC_IBUF_INDEX_TREE);
+#ifdef BTR_CUR_ADAPT
+	ibuf.index->search_info = btr_search_info_create(ibuf.index->heap);
+#endif /* BTR_CUR_ADAPT */
+	ibuf.index->page = FSP_IBUF_TREE_ROOT_PAGE_NO;
+	ut_d(ibuf.index->cached = TRUE);
+
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+	if (!ibuf_dump) {
+		return DB_SUCCESS;
+	}
+	ib::info() << "Dumping the change buffer";
+	ibuf_mtr_start(&mtr);
+	btr_pcur_t pcur;
+	if (DB_SUCCESS == btr_pcur_open_at_index_side(
+		    true, ibuf.index, BTR_SEARCH_LEAF, &pcur,
+		    true, 0, &mtr)) {
+		while (btr_pcur_move_to_next_user_rec(&pcur, &mtr)) {
+			rec_print_old(stderr, btr_pcur_get_rec(&pcur));
+		}
+	}
+	ibuf_mtr_commit(&mtr);
+	ib::info() << "Dumped the change buffer";
+#endif
+
+	return DB_SUCCESS;
+}
+
+/*********************************************************************//**
+Updates the max_size value for ibuf. */
+void
+ibuf_max_size_update(
+/*=================*/
+	ulint	new_val)	/*!< in: new value in terms of
+				percentage of the buffer pool size */
+{
+	ulint	new_size = ((buf_pool_get_curr_size() >> srv_page_size_shift)
+			    * new_val) / 100;
+	mutex_enter(&ibuf_mutex);
+	ibuf.max_size = new_size;
+	mutex_exit(&ibuf_mutex);
+}
+
+# ifdef UNIV_DEBUG
+/** Gets the desired bits for a given page from a bitmap page.
+@param[in]	page		bitmap page
+@param[in]	page_id		page id whose bits to get
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in]	bit		IBUF_BITMAP_FREE, IBUF_BITMAP_BUFFERED, ...
+@param[in,out]	mtr		mini-transaction holding an x-latch on the
+bitmap page
+@return value of bits */
+#  define ibuf_bitmap_page_get_bits(page, page_id, zip_size, bit, mtr)	\
+	ibuf_bitmap_page_get_bits_low(page, page_id, zip_size,		\
+				      MTR_MEMO_PAGE_X_FIX, mtr, bit)
+# else /* UNIV_DEBUG */
+/** Gets the desired bits for a given page from a bitmap page.
+@param[in]	page		bitmap page
+@param[in]	page_id		page id whose bits to get
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in]	bit		IBUF_BITMAP_FREE, IBUF_BITMAP_BUFFERED, ...
+@param[in,out]	mtr		mini-transaction holding an x-latch on the
+bitmap page
+@return value of bits */
+#  define ibuf_bitmap_page_get_bits(page, page_id, zip_size, bit, mtr)	\
+	ibuf_bitmap_page_get_bits_low(page, page_id, zip_size, bit)
+# endif /* UNIV_DEBUG */
+
+/** Gets the desired bits for a given page from a bitmap page.
+@param[in]	page		bitmap page
+@param[in]	page_id		page id whose bits to get
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in]	latch_type	MTR_MEMO_PAGE_X_FIX, MTR_MEMO_BUF_FIX, ...
+@param[in,out]	mtr		mini-transaction holding latch_type on the
+bitmap page
+@param[in]	bit		IBUF_BITMAP_FREE, IBUF_BITMAP_BUFFERED, ...
+@return value of bits */
+UNIV_INLINE
+ulint
+ibuf_bitmap_page_get_bits_low(
+	const page_t*		page,
+	const page_id_t		page_id,
+	ulint			zip_size,
+#ifdef UNIV_DEBUG
+	ulint			latch_type,
+	mtr_t*			mtr,
+#endif /* UNIV_DEBUG */
+	ulint			bit)
+{
+	ulint	byte_offset;
+	ulint	bit_offset;
+	ulint	map_byte;
+	ulint	value;
+	const ulint size = zip_size ? zip_size : srv_page_size;
+
+	ut_ad(ut_is_2pow(zip_size));
+	ut_ad(bit < IBUF_BITS_PER_PAGE);
+	compile_time_assert(!(IBUF_BITS_PER_PAGE % 2));
+	ut_ad(mtr->memo_contains_page_flagged(page, latch_type));
+
+	bit_offset = (page_id.page_no() & (size - 1))
+		* IBUF_BITS_PER_PAGE + bit;
+
+	byte_offset = bit_offset / 8;
+	bit_offset = bit_offset % 8;
+
+	ut_ad(byte_offset + IBUF_BITMAP < srv_page_size);
+
+	map_byte = mach_read_from_1(page + IBUF_BITMAP + byte_offset);
+
+	value = ut_bit_get_nth(map_byte, bit_offset);
+
+	if (bit == IBUF_BITMAP_FREE) {
+		ut_ad(bit_offset + 1 < 8);
+
+		value = value * 2 + ut_bit_get_nth(map_byte, bit_offset + 1);
+	}
+
+	return(value);
+}
+
+/** Sets the desired bit for a given page in a bitmap page.
+@tparam bit	IBUF_BITMAP_FREE, IBUF_BITMAP_BUFFERED, ...
+@param[in,out]	block		bitmap page
+@param[in]	page_id		page id whose bits to set
+@param[in]	physical_size	page size
+@param[in]	val		value to set
+@param[in,out]	mtr		mtr containing an x-latch to the bitmap page */
+template<ulint bit>
+static void
+ibuf_bitmap_page_set_bits(
+	buf_block_t*		block,
+	const page_id_t		page_id,
+	ulint			physical_size,
+	ulint			val,
+	mtr_t*			mtr)
+{
+	ulint	byte_offset;
+	ulint	bit_offset;
+
+	static_assert(bit < IBUF_BITS_PER_PAGE, "wrong bit");
+	compile_time_assert(!(IBUF_BITS_PER_PAGE % 2));
+	ut_ad(mtr->memo_contains_flagged(block, MTR_MEMO_PAGE_X_FIX));
+	ut_ad(mtr->is_named_space(page_id.space()));
+
+	bit_offset = (page_id.page_no() % physical_size)
+		* IBUF_BITS_PER_PAGE + bit;
+
+	byte_offset = bit_offset / 8;
+	bit_offset = bit_offset % 8;
+
+	ut_ad(byte_offset + IBUF_BITMAP < srv_page_size);
+
+	byte* map_byte = &block->frame[IBUF_BITMAP + byte_offset];
+	byte b = *map_byte;
+
+	if (bit == IBUF_BITMAP_FREE) {
+		ut_ad(bit_offset + 1 < 8);
+		ut_ad(val <= 3);
+		b &= static_cast<byte>(~(3U << bit_offset));
+		b |= static_cast<byte>(((val & 2) >> 1) << bit_offset
+				       | (val & 1) << (bit_offset + 1));
+	} else {
+		ut_ad(val <= 1);
+		b &= static_cast<byte>(~(1U << bit_offset));
+#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion" /* GCC 5 may need this here */
+#endif
+		b |= static_cast<byte>(val << bit_offset);
+#if defined __GNUC__ && !defined __clang__ && __GNUC__ < 6
+# pragma GCC diagnostic pop
+#endif
+	}
+
+	mtr->write<1,mtr_t::MAYBE_NOP>(*block, map_byte, b);
+}
+
+/** Calculates the bitmap page number for a given page number.
+@param[in]	page_id		page id
+@param[in]	size		page size
+@return the bitmap page id where the file page is mapped */
+inline page_id_t ibuf_bitmap_page_no_calc(const page_id_t page_id, ulint size)
+{
+  if (!size)
+    size= srv_page_size;
+
+  return page_id_t(page_id.space(), FSP_IBUF_BITMAP_OFFSET
+		   + uint32_t(page_id.page_no() & ~(size - 1)));
+}
+
+/** Gets the ibuf bitmap page where the bits describing a given file page are
+stored.
+@param[in]	page_id		page id of the file page
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in]	file		file name
+@param[in]	line		line where called
+@param[in,out]	mtr		mini-transaction
+@return bitmap page where the file page is mapped, that is, the bitmap
+page containing the descriptor bits for the file page; the bitmap page
+is x-latched */
+static
+buf_block_t*
+ibuf_bitmap_get_map_page_func(
+	const page_id_t		page_id,
+	ulint			zip_size,
+	const char*		file,
+	unsigned		line,
+	mtr_t*			mtr)
+{
+	buf_block_t* block = buf_page_get_gen(
+		ibuf_bitmap_page_no_calc(page_id, zip_size),
+		zip_size, RW_X_LATCH, NULL, BUF_GET_POSSIBLY_FREED,
+		file, line, mtr);
+
+	if (block) {
+		buf_block_dbg_add_level(block, SYNC_IBUF_BITMAP);
+	}
+
+	return block;
+}
+
+/** Gets the ibuf bitmap page where the bits describing a given file page are
+stored.
+@param[in]	page_id		page id of the file page
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in,out]	mtr		mini-transaction
+@return bitmap page where the file page is mapped, that is, the bitmap
+page containing the descriptor bits for the file page; the bitmap page
+is x-latched */
+#define ibuf_bitmap_get_map_page(page_id, zip_size, mtr)	\
+	ibuf_bitmap_get_map_page_func(page_id, zip_size, \
+				      __FILE__, __LINE__, mtr)
+
+/************************************************************************//**
+Sets the free bits of the page in the ibuf bitmap. This is done in a separate
+mini-transaction, hence this operation does not restrict further work to only
+ibuf bitmap operations, which would result if the latch to the bitmap page
+were kept. */
+UNIV_INLINE
+void
+ibuf_set_free_bits_low(
+/*===================*/
+	const buf_block_t*	block,	/*!< in: index page; free bits are set if
+					the index is non-clustered and page
+					level is 0 */
+	ulint			val,	/*!< in: value to set: < 4 */
+	mtr_t*			mtr)	/*!< in/out: mtr */
+{
+	ut_ad(mtr->is_named_space(block->page.id().space()));
+	if (!page_is_leaf(block->frame)) {
+		return;
+	}
+
+#ifdef UNIV_IBUF_DEBUG
+	ut_a(val <= ibuf_index_page_calc_free(block));
+#endif /* UNIV_IBUF_DEBUG */
+	const page_id_t id(block->page.id());
+
+	if (buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(
+			id, block->zip_size(), mtr)) {
+		ibuf_bitmap_page_set_bits<IBUF_BITMAP_FREE>(
+			bitmap_page, id, block->physical_size(),
+			val, mtr);
+	}
+}
+
+/************************************************************************//**
+Sets the free bit of the page in the ibuf bitmap. This is done in a separate
+mini-transaction, hence this operation does not restrict further work to only
+ibuf bitmap operations, which would result if the latch to the bitmap page
+were kept. */
+void
+ibuf_set_free_bits_func(
+/*====================*/
+	buf_block_t*	block,	/*!< in: index page of a non-clustered index;
+				free bit is reset if page level is 0 */
+#ifdef UNIV_IBUF_DEBUG
+	ulint		max_val,/*!< in: ULINT_UNDEFINED or a maximum
+				value which the bits must have before
+				setting; this is for debugging */
+#endif /* UNIV_IBUF_DEBUG */
+	ulint		val)	/*!< in: value to set: < 4 */
+{
+	if (!page_is_leaf(block->frame)) {
+		return;
+	}
+
+	mtr_t	mtr;
+	mtr.start();
+	const page_id_t id(block->page.id());
+
+	const fil_space_t* space = mtr.set_named_space_id(id.space());
+
+	buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(id,
+							    block->zip_size(),
+							    &mtr);
+
+	if (space->purpose != FIL_TYPE_TABLESPACE) {
+		mtr.set_log_mode(MTR_LOG_NO_REDO);
+	}
+
+#ifdef UNIV_IBUF_DEBUG
+	if (max_val != ULINT_UNDEFINED) {
+		ulint	old_val;
+
+		old_val = ibuf_bitmap_page_get_bits(
+			bitmap_page, id,
+			IBUF_BITMAP_FREE, &mtr);
+		ut_a(old_val <= max_val);
+	}
+
+	ut_a(val <= ibuf_index_page_calc_free(block));
+#endif /* UNIV_IBUF_DEBUG */
+
+	ibuf_bitmap_page_set_bits<IBUF_BITMAP_FREE>(
+		bitmap_page, id, block->physical_size(),
+		val, &mtr);
+
+	mtr.commit();
+}
+
+/************************************************************************//**
+Resets the free bits of the page in the ibuf bitmap. This is done in a
+separate mini-transaction, hence this operation does not restrict
+further work to only ibuf bitmap operations, which would result if the
+latch to the bitmap page were kept.  NOTE: The free bits in the insert
+buffer bitmap must never exceed the free space on a page.  It is safe
+to decrement or reset the bits in the bitmap in a mini-transaction
+that is committed before the mini-transaction that affects the free
+space. */
+void
+ibuf_reset_free_bits(
+/*=================*/
+	buf_block_t*	block)	/*!< in: index page; free bits are set to 0
+				if the index is a non-clustered
+				non-unique, and page level is 0 */
+{
+	ibuf_set_free_bits(block, 0, ULINT_UNDEFINED);
+}
+
+/**********************************************************************//**
+Updates the free bits for an uncompressed page to reflect the present
+state.  Does this in the mtr given, which means that the latching
+order rules virtually prevent any further operations for this OS
+thread until mtr is committed.  NOTE: The free bits in the insert
+buffer bitmap must never exceed the free space on a page.  It is safe
+to set the free bits in the same mini-transaction that updated the
+page. */
+void
+ibuf_update_free_bits_low(
+/*======================*/
+	const buf_block_t*	block,		/*!< in: index page */
+	ulint			max_ins_size,	/*!< in: value of
+						maximum insert size
+						with reorganize before
+						the latest operation
+						performed to the page */
+	mtr_t*			mtr)		/*!< in/out: mtr */
+{
+	ulint	before;
+	ulint	after;
+
+	ut_a(!is_buf_block_get_page_zip(block));
+	ut_ad(mtr->is_named_space(block->page.id().space()));
+
+	before = ibuf_index_page_calc_free_bits(srv_page_size,
+						max_ins_size);
+
+	after = ibuf_index_page_calc_free(block);
+
+	/* This approach cannot be used on compressed pages, since the
+	computed value of "before" often does not match the current
+	state of the bitmap.  This is because the free space may
+	increase or decrease when a compressed page is reorganized. */
+	if (before != after) {
+		ibuf_set_free_bits_low(block, after, mtr);
+	}
+}
+
+/**********************************************************************//**
+Updates the free bits for a compressed page to reflect the present
+state.  Does this in the mtr given, which means that the latching
+order rules virtually prevent any further operations for this OS
+thread until mtr is committed.  NOTE: The free bits in the insert
+buffer bitmap must never exceed the free space on a page.  It is safe
+to set the free bits in the same mini-transaction that updated the
+page. */
+void
+ibuf_update_free_bits_zip(
+/*======================*/
+	buf_block_t*	block,	/*!< in/out: index page */
+	mtr_t*		mtr)	/*!< in/out: mtr */
+{
+	ut_ad(page_is_leaf(block->frame));
+	ut_ad(block->zip_size());
+
+	ulint after = ibuf_index_page_calc_free_zip(block);
+
+	if (after == 0) {
+		/* We move the page to the front of the buffer pool LRU list:
+		the purpose of this is to prevent those pages to which we
+		cannot make inserts using the insert buffer from slipping
+		out of the buffer pool */
+
+		buf_page_make_young(&block->page);
+	}
+
+	if (buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(
+		block->page.id(), block->zip_size(), mtr)) {
+
+		ibuf_bitmap_page_set_bits<IBUF_BITMAP_FREE>(
+			bitmap_page, block->page.id(),
+			block->physical_size(), after, mtr);
+	}
+}
+
+/**********************************************************************//**
+Updates the free bits for the two pages to reflect the present state.
+Does this in the mtr given, which means that the latching order rules
+virtually prevent any further operations until mtr is committed.
+NOTE: The free bits in the insert buffer bitmap must never exceed the
+free space on a page.  It is safe to set the free bits in the same
+mini-transaction that updated the pages. */
+void
+ibuf_update_free_bits_for_two_pages_low(
+/*====================================*/
+	buf_block_t*	block1,	/*!< in: index page */
+	buf_block_t*	block2,	/*!< in: index page */
+	mtr_t*		mtr)	/*!< in: mtr */
+{
+	ulint	state;
+
+	ut_ad(mtr->is_named_space(block1->page.id().space()));
+	ut_ad(block1->page.id().space() == block2->page.id().space());
+
+	/* As we have to x-latch two random bitmap pages, we have to acquire
+	the bitmap mutex to prevent a deadlock with a similar operation
+	performed by another OS thread. */
+
+	mutex_enter(&ibuf_bitmap_mutex);
+
+	state = ibuf_index_page_calc_free(block1);
+
+	ibuf_set_free_bits_low(block1, state, mtr);
+
+	state = ibuf_index_page_calc_free(block2);
+
+	ibuf_set_free_bits_low(block2, state, mtr);
+
+	mutex_exit(&ibuf_bitmap_mutex);
+}
+
+/** Returns TRUE if the page is one of the fixed address ibuf pages.
+@param[in]	page_id		page id
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@return TRUE if a fixed address ibuf i/o page */
+inline bool ibuf_fixed_addr_page(const page_id_t page_id, ulint zip_size)
+{
+	return(page_id == page_id_t(IBUF_SPACE_ID, IBUF_TREE_ROOT_PAGE_NO)
+	       || ibuf_bitmap_page(page_id, zip_size));
+}
+
+/** Checks if a page is a level 2 or 3 page in the ibuf hierarchy of pages.
+Must not be called when recv_no_ibuf_operations==true.
+@param[in]	page_id		page id
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in]	x_latch		FALSE if relaxed check (avoid latching the
+bitmap page)
+@param[in]	file		file name
+@param[in]	line		line where called
+@param[in,out]	mtr		mtr which will contain an x-latch to the
+bitmap page if the page is not one of the fixed address ibuf pages, or NULL,
+in which case a new transaction is created.
+@return TRUE if level 2 or level 3 page */
+bool
+ibuf_page_low(
+	const page_id_t		page_id,
+	ulint			zip_size,
+#ifdef UNIV_DEBUG
+	bool			x_latch,
+#endif /* UNIV_DEBUG */
+	const char*		file,
+	unsigned		line,
+	mtr_t*			mtr)
+{
+	ibool	ret;
+	mtr_t	local_mtr;
+
+	ut_ad(!recv_no_ibuf_operations);
+	ut_ad(x_latch || mtr == NULL);
+
+	if (ibuf_fixed_addr_page(page_id, zip_size)) {
+		return(true);
+	} else if (page_id.space() != IBUF_SPACE_ID) {
+		return(false);
+	}
+
+	compile_time_assert(IBUF_SPACE_ID == 0);
+	ut_ad(fil_system.sys_space->purpose == FIL_TYPE_TABLESPACE);
+
+#ifdef UNIV_DEBUG
+	if (!x_latch) {
+		mtr_start(&local_mtr);
+
+		/* Get the bitmap page without a page latch, so that
+		we will not be violating the latching order when
+		another bitmap page has already been latched by this
+		thread. The page will be buffer-fixed, and thus it
+		cannot be removed or relocated while we are looking at
+		it. The contents of the page could change, but the
+		IBUF_BITMAP_IBUF bit that we are interested in should
+		not be modified by any other thread. Nobody should be
+		calling ibuf_add_free_page() or ibuf_remove_free_page()
+		while the page is linked to the insert buffer b-tree. */
+		dberr_t err = DB_SUCCESS;
+
+		buf_block_t* block = buf_page_get_gen(
+			ibuf_bitmap_page_no_calc(page_id, zip_size),
+			zip_size, RW_NO_LATCH, NULL, BUF_GET_NO_LATCH,
+			file, line, &local_mtr, &err);
+
+		ret = ibuf_bitmap_page_get_bits_low(
+			block->frame, page_id, zip_size,
+			MTR_MEMO_BUF_FIX, &local_mtr, IBUF_BITMAP_IBUF);
+
+		mtr_commit(&local_mtr);
+		return(ret);
+	}
+#endif /* UNIV_DEBUG */
+
+	if (mtr == NULL) {
+		mtr = &local_mtr;
+		mtr_start(mtr);
+	}
+
+	ret = ibuf_bitmap_page_get_bits(ibuf_bitmap_get_map_page_func(
+						page_id, zip_size, file, line,
+						mtr)->frame,
+					page_id, zip_size,
+					IBUF_BITMAP_IBUF, mtr);
+
+	if (mtr == &local_mtr) {
+		mtr_commit(mtr);
+	}
+
+	return(ret);
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_rec_get_page_no(mtr,rec) ibuf_rec_get_page_no_func(mtr,rec)
+#else /* UNIV_DEBUG */
+# define ibuf_rec_get_page_no(mtr,rec) ibuf_rec_get_page_no_func(rec)
+#endif /* UNIV_DEBUG */
+
+/********************************************************************//**
+Returns the page number field of an ibuf record.
+@return page number */
+static
+uint32_t
+ibuf_rec_get_page_no_func(
+/*======================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction owning rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	rec)	/*!< in: ibuf record */
+{
+	const byte*	field;
+	ulint		len;
+
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(rec_get_n_fields_old(rec) > 2);
+
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_MARKER, &len);
+
+	ut_a(len == 1);
+
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_PAGE, &len);
+
+	ut_a(len == 4);
+
+	return(mach_read_from_4(field));
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_rec_get_space(mtr,rec) ibuf_rec_get_space_func(mtr,rec)
+#else /* UNIV_DEBUG */
+# define ibuf_rec_get_space(mtr,rec) ibuf_rec_get_space_func(rec)
+#endif /* UNIV_DEBUG */
+
+/********************************************************************//**
+Returns the space id field of an ibuf record. For < 4.1.x format records
+returns 0.
+@return space id */
+static
+uint32_t
+ibuf_rec_get_space_func(
+/*====================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction owning rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	rec)	/*!< in: ibuf record */
+{
+	const byte*	field;
+	ulint		len;
+
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(rec_get_n_fields_old(rec) > 2);
+
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_MARKER, &len);
+
+	ut_a(len == 1);
+
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_SPACE, &len);
+
+	ut_a(len == 4);
+
+	return(mach_read_from_4(field));
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_rec_get_info(mtr,rec,op,comp,info_len,counter)	\
+	ibuf_rec_get_info_func(mtr,rec,op,comp,info_len,counter)
+#else /* UNIV_DEBUG */
+# define ibuf_rec_get_info(mtr,rec,op,comp,info_len,counter)	\
+	ibuf_rec_get_info_func(rec,op,comp,info_len,counter)
+#endif
+/****************************************************************//**
+Get various information about an ibuf record in >= 4.1.x format. */
+static
+void
+ibuf_rec_get_info_func(
+/*===================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction owning rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	rec,		/*!< in: ibuf record */
+	ibuf_op_t*	op,		/*!< out: operation type, or NULL */
+	ibool*		comp,		/*!< out: compact flag, or NULL */
+	ulint*		info_len,	/*!< out: length of info fields at the
+					start of the fourth field, or
+					NULL */
+	ulint*		counter)	/*!< in: counter value, or NULL */
+{
+	const byte*	types;
+	ulint		fields;
+	ulint		len;
+
+	/* Local variables to shadow arguments. */
+	ibuf_op_t	op_local;
+	ibool		comp_local;
+	ulint		info_len_local;
+	ulint		counter_local;
+
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+	fields = rec_get_n_fields_old(rec);
+	ut_a(fields > IBUF_REC_FIELD_USER);
+
+	types = rec_get_nth_field_old(rec, IBUF_REC_FIELD_METADATA, &len);
+
+	info_len_local = len % DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE;
+	compile_time_assert(IBUF_REC_INFO_SIZE
+			    < DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE);
+
+	switch (info_len_local) {
+	case 0:
+	case 1:
+		op_local = IBUF_OP_INSERT;
+		comp_local = info_len_local;
+		ut_ad(!counter);
+		counter_local = ULINT_UNDEFINED;
+		break;
+
+	case IBUF_REC_INFO_SIZE:
+		op_local = (ibuf_op_t) types[IBUF_REC_OFFSET_TYPE];
+		comp_local = types[IBUF_REC_OFFSET_FLAGS] & IBUF_REC_COMPACT;
+		counter_local = mach_read_from_2(
+			types + IBUF_REC_OFFSET_COUNTER);
+		break;
+
+	default:
+		ut_error;
+	}
+
+	ut_a(op_local < IBUF_OP_COUNT);
+	ut_a((len - info_len_local) ==
+	     (fields - IBUF_REC_FIELD_USER)
+	     * DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE);
+
+	if (op) {
+		*op = op_local;
+	}
+
+	if (comp) {
+		*comp = comp_local;
+	}
+
+	if (info_len) {
+		*info_len = info_len_local;
+	}
+
+	if (counter) {
+		*counter = counter_local;
+	}
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_rec_get_op_type(mtr,rec) ibuf_rec_get_op_type_func(mtr,rec)
+#else /* UNIV_DEBUG */
+# define ibuf_rec_get_op_type(mtr,rec) ibuf_rec_get_op_type_func(rec)
+#endif
+
+/****************************************************************//**
+Returns the operation type field of an ibuf record.
+@return operation type */
+static
+ibuf_op_t
+ibuf_rec_get_op_type_func(
+/*======================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction owning rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	rec)	/*!< in: ibuf record */
+{
+	ulint		len;
+
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(rec_get_n_fields_old(rec) > 2);
+
+	(void) rec_get_nth_field_old(rec, IBUF_REC_FIELD_MARKER, &len);
+
+	if (len > 1) {
+		/* This is a < 4.1.x format record */
+
+		return(IBUF_OP_INSERT);
+	} else {
+		ibuf_op_t	op;
+
+		ibuf_rec_get_info(mtr, rec, &op, NULL, NULL, NULL);
+
+		return(op);
+	}
+}
+
+/****************************************************************//**
+Read the first two bytes from a record's fourth field (counter field in new
+records; something else in older records).
+@return "counter" field, or ULINT_UNDEFINED if for some reason it
+can't be read */
+ulint
+ibuf_rec_get_counter(
+/*=================*/
+	const rec_t*	rec)	/*!< in: ibuf record */
+{
+	const byte*	ptr;
+	ulint		len;
+
+	if (rec_get_n_fields_old(rec) <= IBUF_REC_FIELD_METADATA) {
+
+		return(ULINT_UNDEFINED);
+	}
+
+	ptr = rec_get_nth_field_old(rec, IBUF_REC_FIELD_METADATA, &len);
+
+	if (len >= 2) {
+
+		return(mach_read_from_2(ptr));
+	} else {
+
+		return(ULINT_UNDEFINED);
+	}
+}
+
+
+/**
+  Add accumulated operation counts to a permanent array.
+  Both arrays must be of size IBUF_OP_COUNT.
+*/
+static void ibuf_add_ops(Atomic_counter<ulint> *out, const ulint *in)
+{
+  for (auto i = 0; i < IBUF_OP_COUNT; i++)
+    out[i]+= in[i];
+}
+
+
+/****************************************************************//**
+Print operation counts. The array must be of size IBUF_OP_COUNT. */
+static
+void
+ibuf_print_ops(
+/*===========*/
+	const Atomic_counter<ulint>*	ops,	/*!< in: operation counts */
+	FILE*				file)	/*!< in: file where to print */
+{
+	static const char* op_names[] = {
+		"insert",
+		"delete mark",
+		"delete"
+	};
+	ulint	i;
+
+	ut_a(UT_ARR_SIZE(op_names) == IBUF_OP_COUNT);
+
+	for (i = 0; i < IBUF_OP_COUNT; i++) {
+		fprintf(file, "%s " ULINTPF "%s", op_names[i],
+			ulint{ops[i]}, (i < (IBUF_OP_COUNT - 1)) ? ", " : "");
+	}
+
+	putc('\n', file);
+}
+
+/********************************************************************//**
+Creates a dummy index for inserting a record to a non-clustered index.
+@return dummy index */
+static
+dict_index_t*
+ibuf_dummy_index_create(
+/*====================*/
+	ulint		n,	/*!< in: number of fields */
+	ibool		comp)	/*!< in: TRUE=use compact record format */
+{
+	dict_table_t*	table;
+	dict_index_t*	index;
+
+	table = dict_mem_table_create("IBUF_DUMMY", NULL, n, 0,
+				      comp ? DICT_TF_COMPACT : 0, 0);
+
+	index = dict_mem_index_create(table, "IBUF_DUMMY", 0, n);
+
+	/* avoid ut_ad(index->cached) in dict_index_get_n_unique_in_tree */
+	index->cached = TRUE;
+	ut_d(index->is_dummy = true);
+
+	return(index);
+}
+/********************************************************************//**
+Add a column to the dummy index */
+static
+void
+ibuf_dummy_index_add_col(
+/*=====================*/
+	dict_index_t*	index,	/*!< in: dummy index */
+	const dtype_t*	type,	/*!< in: the data type of the column */
+	ulint		len)	/*!< in: length of the column */
+{
+	ulint	i	= index->table->n_def;
+	dict_mem_table_add_col(index->table, NULL, NULL,
+			       dtype_get_mtype(type),
+			       dtype_get_prtype(type),
+			       dtype_get_len(type));
+	dict_index_add_col(index, index->table,
+			   dict_table_get_nth_col(index->table, i), len);
+}
+/********************************************************************//**
+Deallocates a dummy index for inserting a record to a non-clustered index. */
+static
+void
+ibuf_dummy_index_free(
+/*==================*/
+	dict_index_t*	index)	/*!< in, own: dummy index */
+{
+	dict_table_t*	table = index->table;
+
+	dict_mem_index_free(index);
+	dict_mem_table_free(table);
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_build_entry_from_ibuf_rec(mtr,ibuf_rec,heap,pindex)	\
+	ibuf_build_entry_from_ibuf_rec_func(mtr,ibuf_rec,heap,pindex)
+#else /* UNIV_DEBUG */
+# define ibuf_build_entry_from_ibuf_rec(mtr,ibuf_rec,heap,pindex)	\
+	ibuf_build_entry_from_ibuf_rec_func(ibuf_rec,heap,pindex)
+#endif
+
+/*********************************************************************//**
+Builds the entry used to
+
+1) IBUF_OP_INSERT: insert into a non-clustered index
+
+2) IBUF_OP_DELETE_MARK: find the record whose delete-mark flag we need to
+   activate
+
+3) IBUF_OP_DELETE: find the record we need to delete
+
+when we have the corresponding record in an ibuf index.
+
+NOTE that as we copy pointers to fields in ibuf_rec, the caller must
+hold a latch to the ibuf_rec page as long as the entry is used!
+
+@return own: entry to insert to a non-clustered index */
+static
+dtuple_t*
+ibuf_build_entry_from_ibuf_rec_func(
+/*================================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction owning rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	ibuf_rec,	/*!< in: record in an insert buffer */
+	mem_heap_t*	heap,		/*!< in: heap where built */
+	dict_index_t**	pindex)		/*!< out, own: dummy index that
+					describes the entry */
+{
+	dtuple_t*	tuple;
+	dfield_t*	field;
+	ulint		n_fields;
+	const byte*	types;
+	const byte*	data;
+	ulint		len;
+	ulint		info_len;
+	ulint		i;
+	ulint		comp;
+	dict_index_t*	index;
+
+	ut_ad(mtr->memo_contains_page_flagged(ibuf_rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+
+	data = rec_get_nth_field_old(ibuf_rec, IBUF_REC_FIELD_MARKER, &len);
+
+	ut_a(len == 1);
+	ut_a(*data == 0);
+	ut_a(rec_get_n_fields_old(ibuf_rec) > IBUF_REC_FIELD_USER);
+
+	n_fields = rec_get_n_fields_old(ibuf_rec) - IBUF_REC_FIELD_USER;
+
+	tuple = dtuple_create(heap, n_fields);
+
+	types = rec_get_nth_field_old(ibuf_rec, IBUF_REC_FIELD_METADATA, &len);
+
+	ibuf_rec_get_info(mtr, ibuf_rec, NULL, &comp, &info_len, NULL);
+
+	index = ibuf_dummy_index_create(n_fields, comp);
+
+	len -= info_len;
+	types += info_len;
+
+	ut_a(len == n_fields * DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE);
+
+	for (i = 0; i < n_fields; i++) {
+		field = dtuple_get_nth_field(tuple, i);
+
+		data = rec_get_nth_field_old(
+			ibuf_rec, i + IBUF_REC_FIELD_USER, &len);
+
+		dfield_set_data(field, data, len);
+
+		dtype_new_read_for_order_and_null_size(
+			dfield_get_type(field),
+			types + i * DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE);
+
+		ibuf_dummy_index_add_col(index, dfield_get_type(field), len);
+	}
+
+	index->n_core_null_bytes = static_cast<uint8_t>(
+		UT_BITS_IN_BYTES(unsigned(index->n_nullable)));
+
+	/* Prevent an ut_ad() failure in page_zip_write_rec() by
+	adding system columns to the dummy table pointed to by the
+	dummy secondary index.  The insert buffer is only used for
+	secondary indexes, whose records never contain any system
+	columns, such as DB_TRX_ID. */
+	ut_d(dict_table_add_system_columns(index->table, index->table->heap));
+
+	*pindex = index;
+
+	return(tuple);
+}
+
+/******************************************************************//**
+Get the data size.
+@return size of fields */
+UNIV_INLINE
+ulint
+ibuf_rec_get_size(
+/*==============*/
+	const rec_t*	rec,			/*!< in: ibuf record */
+	const byte*	types,			/*!< in: fields */
+	ulint		n_fields,		/*!< in: number of fields */
+	ulint		comp)			/*!< in: 0=ROW_FORMAT=REDUNDANT,
+						nonzero=ROW_FORMAT=COMPACT */
+{
+	ulint	i;
+	ulint	field_offset;
+	ulint	types_offset;
+	ulint	size = 0;
+
+	field_offset = IBUF_REC_FIELD_USER;
+	types_offset = DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE;
+
+	for (i = 0; i < n_fields; i++) {
+		ulint		len;
+		dtype_t		dtype;
+
+		rec_get_nth_field_offs_old(rec, i + field_offset, &len);
+
+		if (len != UNIV_SQL_NULL) {
+			size += len;
+		} else {
+			dtype_new_read_for_order_and_null_size(&dtype, types);
+
+			size += dtype_get_sql_null_size(&dtype, comp);
+		}
+
+		types += types_offset;
+	}
+
+	return(size);
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_rec_get_volume(mtr,rec) ibuf_rec_get_volume_func(mtr,rec)
+#else /* UNIV_DEBUG */
+# define ibuf_rec_get_volume(mtr,rec) ibuf_rec_get_volume_func(rec)
+#endif
+
+/********************************************************************//**
+Returns the space taken by a stored non-clustered index entry if converted to
+an index record.
+@return size of index record in bytes + an upper limit of the space
+taken in the page directory */
+static
+ulint
+ibuf_rec_get_volume_func(
+/*=====================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction owning rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	ibuf_rec)/*!< in: ibuf record */
+{
+	ulint		len;
+	const byte*	data;
+	const byte*	types;
+	ulint		n_fields;
+	ulint		data_size;
+	ulint		comp;
+	ibuf_op_t	op;
+	ulint		info_len;
+
+	ut_ad(mtr->memo_contains_page_flagged(ibuf_rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(rec_get_n_fields_old(ibuf_rec) > 2);
+
+	data = rec_get_nth_field_old(ibuf_rec, IBUF_REC_FIELD_MARKER, &len);
+	ut_a(len == 1);
+	ut_a(*data == 0);
+
+	types = rec_get_nth_field_old(
+		ibuf_rec, IBUF_REC_FIELD_METADATA, &len);
+
+	ibuf_rec_get_info(mtr, ibuf_rec, &op, &comp, &info_len, NULL);
+
+	if (op == IBUF_OP_DELETE_MARK || op == IBUF_OP_DELETE) {
+		/* Delete-marking a record doesn't take any
+		additional space, and while deleting a record
+		actually frees up space, we have to play it safe and
+		pretend it takes no additional space (the record
+		might not exist, etc.).  */
+
+		return(0);
+	} else if (comp) {
+		dtuple_t*	entry;
+		ulint		volume;
+		dict_index_t*	dummy_index;
+		mem_heap_t*	heap = mem_heap_create(500);
+
+		entry = ibuf_build_entry_from_ibuf_rec(mtr, ibuf_rec,
+			heap, &dummy_index);
+
+		volume = rec_get_converted_size(dummy_index, entry, 0);
+
+		ibuf_dummy_index_free(dummy_index);
+		mem_heap_free(heap);
+
+		return(volume + page_dir_calc_reserved_space(1));
+	}
+
+	types += info_len;
+	n_fields = rec_get_n_fields_old(ibuf_rec)
+		- IBUF_REC_FIELD_USER;
+
+	data_size = ibuf_rec_get_size(ibuf_rec, types, n_fields, comp);
+
+	return(data_size + rec_get_converted_extra_size(data_size, n_fields, 0)
+	       + page_dir_calc_reserved_space(1));
+}
+
+/*********************************************************************//**
+Builds the tuple to insert to an ibuf tree when we have an entry for a
+non-clustered index.
+
+NOTE that the original entry must be kept because we copy pointers to
+its fields.
+
+@return own: entry to insert into an ibuf index tree */
+static
+dtuple_t*
+ibuf_entry_build(
+/*=============*/
+	ibuf_op_t	op,	/*!< in: operation type */
+	dict_index_t*	index,	/*!< in: non-clustered index */
+	const dtuple_t*	entry,	/*!< in: entry for a non-clustered index */
+	ulint		space,	/*!< in: space id */
+	ulint		page_no,/*!< in: index page number where entry should
+				be inserted */
+	ulint		counter,/*!< in: counter value;
+				ULINT_UNDEFINED=not used */
+	mem_heap_t*	heap)	/*!< in: heap into which to build */
+{
+	dtuple_t*	tuple;
+	dfield_t*	field;
+	const dfield_t*	entry_field;
+	ulint		n_fields;
+	byte*		buf;
+	byte*		ti;
+	byte*		type_info;
+	ulint		i;
+
+	ut_ad(counter != ULINT_UNDEFINED || op == IBUF_OP_INSERT);
+	ut_ad(counter == ULINT_UNDEFINED || counter <= 0xFFFF);
+	ut_ad(op < IBUF_OP_COUNT);
+
+	/* We have to build a tuple with the following fields:
+
+	1-4) These are described at the top of this file.
+
+	5) The rest of the fields are copied from the entry.
+
+	All fields in the tuple are ordered like the type binary in our
+	insert buffer tree. */
+
+	n_fields = dtuple_get_n_fields(entry);
+
+	tuple = dtuple_create(heap, n_fields + IBUF_REC_FIELD_USER);
+
+	/* 1) Space Id */
+
+	field = dtuple_get_nth_field(tuple, IBUF_REC_FIELD_SPACE);
+
+	buf = static_cast<byte*>(mem_heap_alloc(heap, 4));
+
+	mach_write_to_4(buf, space);
+
+	dfield_set_data(field, buf, 4);
+
+	/* 2) Marker byte */
+
+	field = dtuple_get_nth_field(tuple, IBUF_REC_FIELD_MARKER);
+
+	buf = static_cast<byte*>(mem_heap_alloc(heap, 1));
+
+	/* We set the marker byte zero */
+
+	mach_write_to_1(buf, 0);
+
+	dfield_set_data(field, buf, 1);
+
+	/* 3) Page number */
+
+	field = dtuple_get_nth_field(tuple, IBUF_REC_FIELD_PAGE);
+
+	buf = static_cast<byte*>(mem_heap_alloc(heap, 4));
+
+	mach_write_to_4(buf, page_no);
+
+	dfield_set_data(field, buf, 4);
+
+	/* 4) Type info, part #1 */
+
+	if (counter == ULINT_UNDEFINED) {
+		i = dict_table_is_comp(index->table) ? 1 : 0;
+	} else {
+		ut_ad(counter <= 0xFFFF);
+		i = IBUF_REC_INFO_SIZE;
+	}
+
+	ti = type_info = static_cast<byte*>(
+		mem_heap_alloc(
+			heap,
+			i + n_fields * DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE));
+
+	switch (i) {
+	default:
+		ut_error;
+		break;
+	case 1:
+		/* set the flag for ROW_FORMAT=COMPACT */
+		*ti++ = 0;
+		/* fall through */
+	case 0:
+		/* the old format does not allow delete buffering */
+		ut_ad(op == IBUF_OP_INSERT);
+		break;
+	case IBUF_REC_INFO_SIZE:
+		mach_write_to_2(ti + IBUF_REC_OFFSET_COUNTER, counter);
+
+		ti[IBUF_REC_OFFSET_TYPE] = (byte) op;
+		ti[IBUF_REC_OFFSET_FLAGS] = dict_table_is_comp(index->table)
+			? IBUF_REC_COMPACT : 0;
+		ti += IBUF_REC_INFO_SIZE;
+		break;
+	}
+
+	/* 5+) Fields from the entry */
+
+	for (i = 0; i < n_fields; i++) {
+		ulint			fixed_len;
+		const dict_field_t*	ifield;
+
+		field = dtuple_get_nth_field(tuple, i + IBUF_REC_FIELD_USER);
+		entry_field = dtuple_get_nth_field(entry, i);
+		dfield_copy(field, entry_field);
+
+		ifield = dict_index_get_nth_field(index, i);
+		/* Prefix index columns of fixed-length columns are of
+		fixed length.  However, in the function call below,
+		dfield_get_type(entry_field) contains the fixed length
+		of the column in the clustered index.  Replace it with
+		the fixed length of the secondary index column. */
+		fixed_len = ifield->fixed_len;
+
+#ifdef UNIV_DEBUG
+		if (fixed_len) {
+			/* dict_index_add_col() should guarantee these */
+			ut_ad(fixed_len <= (ulint)
+			      dfield_get_type(entry_field)->len);
+			if (ifield->prefix_len) {
+				ut_ad(ifield->prefix_len == fixed_len);
+			} else {
+				ut_ad(fixed_len == (ulint)
+				      dfield_get_type(entry_field)->len);
+			}
+		}
+#endif /* UNIV_DEBUG */
+
+		dtype_new_store_for_order_and_null_size(
+			ti, dfield_get_type(entry_field), fixed_len);
+		ti += DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE;
+	}
+
+	/* 4) Type info, part #2 */
+
+	field = dtuple_get_nth_field(tuple, IBUF_REC_FIELD_METADATA);
+
+	dfield_set_data(field, type_info, ulint(ti - type_info));
+
+	/* Set all the types in the new tuple binary */
+
+	dtuple_set_types_binary(tuple, n_fields + IBUF_REC_FIELD_USER);
+
+	return(tuple);
+}
+
+/*********************************************************************//**
+Builds a search tuple used to search buffered inserts for an index page.
+This is for >= 4.1.x format records.
+@return own: search tuple */
+static
+dtuple_t*
+ibuf_search_tuple_build(
+/*====================*/
+	ulint		space,	/*!< in: space id */
+	ulint		page_no,/*!< in: index page number */
+	mem_heap_t*	heap)	/*!< in: heap into which to build */
+{
+	dtuple_t*	tuple;
+	dfield_t*	field;
+	byte*		buf;
+
+	tuple = dtuple_create(heap, IBUF_REC_FIELD_METADATA);
+
+	/* Store the space id in tuple */
+
+	field = dtuple_get_nth_field(tuple, IBUF_REC_FIELD_SPACE);
+
+	buf = static_cast<byte*>(mem_heap_alloc(heap, 4));
+
+	mach_write_to_4(buf, space);
+
+	dfield_set_data(field, buf, 4);
+
+	/* Store the new format record marker byte */
+
+	field = dtuple_get_nth_field(tuple, IBUF_REC_FIELD_MARKER);
+
+	buf = static_cast<byte*>(mem_heap_alloc(heap, 1));
+
+	mach_write_to_1(buf, 0);
+
+	dfield_set_data(field, buf, 1);
+
+	/* Store the page number in tuple */
+
+	field = dtuple_get_nth_field(tuple, IBUF_REC_FIELD_PAGE);
+
+	buf = static_cast<byte*>(mem_heap_alloc(heap, 4));
+
+	mach_write_to_4(buf, page_no);
+
+	dfield_set_data(field, buf, 4);
+
+	dtuple_set_types_binary(tuple, IBUF_REC_FIELD_METADATA);
+
+	return(tuple);
+}
+
+/*********************************************************************//**
+Checks if there are enough pages in the free list of the ibuf tree that we
+dare to start a pessimistic insert to the insert buffer.
+@return whether enough free pages in list */
+static inline bool ibuf_data_enough_free_for_insert()
+{
+	ut_ad(mutex_own(&ibuf_mutex));
+
+	/* We want a big margin of free pages, because a B-tree can sometimes
+	grow in size also if records are deleted from it, as the node pointers
+	can change, and we must make sure that we are able to delete the
+	inserts buffered for pages that we read to the buffer pool, without
+	any risk of running out of free space in the insert buffer. */
+
+	return(ibuf.free_list_len >= (ibuf.size / 2) + 3 * ibuf.height);
+}
+
+/*********************************************************************//**
+Checks if there are enough pages in the free list of the ibuf tree that we
+should remove them and free to the file space management.
+@return TRUE if enough free pages in list */
+UNIV_INLINE
+ibool
+ibuf_data_too_much_free(void)
+/*=========================*/
+{
+	ut_ad(mutex_own(&ibuf_mutex));
+
+	return(ibuf.free_list_len >= 3 + (ibuf.size / 2) + 3 * ibuf.height);
+}
+
+/** Allocate a change buffer page.
+@retval true on success
+@retval false if no space left */
+static bool ibuf_add_free_page()
+{
+	mtr_t		mtr;
+	page_t*		header_page;
+	buf_block_t*	block;
+
+	mtr.start();
+	/* Acquire the fsp latch before the ibuf header, obeying the latching
+	order */
+	mtr_x_lock_space(fil_system.sys_space, &mtr);
+	header_page = ibuf_header_page_get(&mtr);
+
+	/* Allocate a new page: NOTE that if the page has been a part of a
+	non-clustered index which has subsequently been dropped, then the
+	page may have buffered inserts in the insert buffer, and these
+	should be deleted from there. These get deleted when the page
+	allocation creates the page in buffer. Thus the call below may end
+	up calling the insert buffer routines and, as we yet have no latches
+	to insert buffer tree pages, these routines can run without a risk
+	of a deadlock. This is the reason why we created a special ibuf
+	header page apart from the ibuf tree. */
+
+	block = fseg_alloc_free_page(
+		header_page + IBUF_HEADER + IBUF_TREE_SEG_HEADER, 0, FSP_UP,
+		&mtr);
+
+	if (block == NULL) {
+		mtr.commit();
+		return false;
+	}
+
+	ut_ad(rw_lock_get_x_lock_count(&block->lock) == 1);
+	ibuf_enter(&mtr);
+	mutex_enter(&ibuf_mutex);
+
+	buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE_NEW);
+
+	mtr.write<2>(*block, block->frame + FIL_PAGE_TYPE,
+		     FIL_PAGE_IBUF_FREE_LIST);
+
+	/* Add the page to the free list and update the ibuf size data */
+
+	flst_add_last(ibuf_tree_root_get(&mtr),
+		      PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST,
+		      block, PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST_NODE, &mtr);
+
+	ibuf.seg_size++;
+	ibuf.free_list_len++;
+
+	/* Set the bit indicating that this page is now an ibuf tree page
+	(level 2 page) */
+
+	const page_id_t page_id(block->page.id());
+	buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(page_id, 0, &mtr);
+
+	mutex_exit(&ibuf_mutex);
+
+	ibuf_bitmap_page_set_bits<IBUF_BITMAP_IBUF>(bitmap_page, page_id,
+						    srv_page_size, true,
+						    &mtr);
+
+	ibuf_mtr_commit(&mtr);
+
+	return true;
+}
+
+/*********************************************************************//**
+Removes a page from the free list and frees it to the fsp system. */
+static
+void
+ibuf_remove_free_page(void)
+/*=======================*/
+{
+	mtr_t	mtr;
+	mtr_t	mtr2;
+	page_t*	header_page;
+
+	log_free_check();
+
+	mtr_start(&mtr);
+	/* Acquire the fsp latch before the ibuf header, obeying the latching
+	order */
+
+	mtr_x_lock_space(fil_system.sys_space, &mtr);
+	header_page = ibuf_header_page_get(&mtr);
+
+	/* Prevent pessimistic inserts to insert buffer trees for a while */
+	ibuf_enter(&mtr);
+	mutex_enter(&ibuf_pessimistic_insert_mutex);
+	mutex_enter(&ibuf_mutex);
+
+	if (!ibuf_data_too_much_free()) {
+
+		mutex_exit(&ibuf_mutex);
+		mutex_exit(&ibuf_pessimistic_insert_mutex);
+
+		ibuf_mtr_commit(&mtr);
+
+		return;
+	}
+
+	ibuf_mtr_start(&mtr2);
+
+	buf_block_t* root = ibuf_tree_root_get(&mtr2);
+
+	mutex_exit(&ibuf_mutex);
+
+	uint32_t page_no = flst_get_last(PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST
+					 + root->frame).page;
+
+	/* NOTE that we must release the latch on the ibuf tree root
+	because in fseg_free_page we access level 1 pages, and the root
+	is a level 2 page. */
+
+	ibuf_mtr_commit(&mtr2);
+	ibuf_exit(&mtr);
+
+	/* Since pessimistic inserts were prevented, we know that the
+	page is still in the free list. NOTE that also deletes may take
+	pages from the free list, but they take them from the start, and
+	the free list was so long that they cannot have taken the last
+	page from it. */
+
+	compile_time_assert(IBUF_SPACE_ID == 0);
+	fseg_free_page(header_page + IBUF_HEADER + IBUF_TREE_SEG_HEADER,
+		       fil_system.sys_space, page_no, &mtr);
+
+	const page_id_t	page_id(IBUF_SPACE_ID, page_no);
+
+	ibuf_enter(&mtr);
+
+	mutex_enter(&ibuf_mutex);
+
+	root = ibuf_tree_root_get(&mtr);
+
+	ut_ad(page_no == flst_get_last(PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST
+				       + root->frame).page);
+
+	buf_block_t* block = buf_page_get(page_id, 0, RW_X_LATCH, &mtr);
+	buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE);
+
+	/* Remove the page from the free list and update the ibuf size data */
+
+	flst_remove(root, PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST,
+		    block, PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST_NODE, &mtr);
+
+	mutex_exit(&ibuf_pessimistic_insert_mutex);
+
+	ibuf.seg_size--;
+	ibuf.free_list_len--;
+
+	/* Set the bit indicating that this page is no more an ibuf tree page
+	(level 2 page) */
+
+	buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(page_id, 0, &mtr);
+
+	mutex_exit(&ibuf_mutex);
+
+	ibuf_bitmap_page_set_bits<IBUF_BITMAP_IBUF>(
+		bitmap_page, page_id, srv_page_size, false, &mtr);
+
+	buf_page_free(fil_system.sys_space, page_no, &mtr, __FILE__, __LINE__);
+
+	ibuf_mtr_commit(&mtr);
+}
+
+/***********************************************************************//**
+Frees excess pages from the ibuf free list. This function is called when an OS
+thread calls fsp services to allocate a new file segment, or a new page to a
+file segment, and the thread did not own the fsp latch before this call. */
+void
+ibuf_free_excess_pages(void)
+/*========================*/
+{
+	/* Free at most a few pages at a time, so that we do not delay the
+	requested service too much */
+
+	for (ulint i = 0; i < 4; i++) {
+
+		ibool	too_much_free;
+
+		mutex_enter(&ibuf_mutex);
+		too_much_free = ibuf_data_too_much_free();
+		mutex_exit(&ibuf_mutex);
+
+		if (!too_much_free) {
+			return;
+		}
+
+		ibuf_remove_free_page();
+	}
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_get_merge_page_nos(contract,rec,mtr,ids,pages,n_stored) \
+	ibuf_get_merge_page_nos_func(contract,rec,mtr,ids,pages,n_stored)
+#else /* UNIV_DEBUG */
+# define ibuf_get_merge_page_nos(contract,rec,mtr,ids,pages,n_stored) \
+	ibuf_get_merge_page_nos_func(contract,rec,ids,pages,n_stored)
+#endif /* UNIV_DEBUG */
+
+/*********************************************************************//**
+Reads page numbers from a leaf in an ibuf tree.
+@return a lower limit for the combined volume of records which will be
+merged */
+static
+ulint
+ibuf_get_merge_page_nos_func(
+/*=========================*/
+	ibool		contract,/*!< in: TRUE if this function is called to
+				contract the tree, FALSE if this is called
+				when a single page becomes full and we look
+				if it pays to read also nearby pages */
+	const rec_t*	rec,	/*!< in: insert buffer record */
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction holding rec */
+#endif /* UNIV_DEBUG */
+	uint32_t*	space_ids,/*!< in/out: space id's of the pages */
+	uint32_t*	page_nos,/*!< in/out: buffer for at least
+				IBUF_MAX_N_PAGES_MERGED many page numbers;
+				the page numbers are in an ascending order */
+	ulint*		n_stored)/*!< out: number of page numbers stored to
+				page_nos in this function */
+{
+	uint32_t prev_page_no;
+	uint32_t prev_space_id;
+	uint32_t first_page_no;
+	uint32_t first_space_id;
+	uint32_t rec_page_no;
+	uint32_t rec_space_id;
+	ulint	sum_volumes;
+	ulint	volume_for_page;
+	ulint	rec_volume;
+	ulint	limit;
+	ulint	n_pages;
+
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+
+	*n_stored = 0;
+
+	limit = ut_min(IBUF_MAX_N_PAGES_MERGED,
+		       buf_pool_get_curr_size() / 4);
+
+	if (page_rec_is_supremum(rec)) {
+
+		rec = page_rec_get_prev_const(rec);
+	}
+
+	if (page_rec_is_infimum(rec)) {
+
+		rec = page_rec_get_next_const(rec);
+	}
+
+	if (page_rec_is_supremum(rec)) {
+
+		return(0);
+	}
+
+	first_page_no = ibuf_rec_get_page_no(mtr, rec);
+	first_space_id = ibuf_rec_get_space(mtr, rec);
+	n_pages = 0;
+	prev_page_no = 0;
+	prev_space_id = 0;
+
+	/* Go backwards from the first rec until we reach the border of the
+	'merge area', or the page start or the limit of storeable pages is
+	reached */
+
+	while (!page_rec_is_infimum(rec) && UNIV_LIKELY(n_pages < limit)) {
+
+		rec_page_no = ibuf_rec_get_page_no(mtr, rec);
+		rec_space_id = ibuf_rec_get_space(mtr, rec);
+
+		if (rec_space_id != first_space_id
+		    || (rec_page_no / IBUF_MERGE_AREA)
+		    != (first_page_no / IBUF_MERGE_AREA)) {
+
+			break;
+		}
+
+		if (rec_page_no != prev_page_no
+		    || rec_space_id != prev_space_id) {
+			n_pages++;
+		}
+
+		prev_page_no = rec_page_no;
+		prev_space_id = rec_space_id;
+
+		rec = page_rec_get_prev_const(rec);
+	}
+
+	rec = page_rec_get_next_const(rec);
+
+	/* At the loop start there is no prev page; we mark this with a pair
+	of space id, page no (0, 0) for which there can never be entries in
+	the insert buffer */
+
+	prev_page_no = 0;
+	prev_space_id = 0;
+	sum_volumes = 0;
+	volume_for_page = 0;
+
+	while (*n_stored < limit) {
+		if (page_rec_is_supremum(rec)) {
+			/* When no more records available, mark this with
+			another 'impossible' pair of space id, page no */
+			rec_page_no = 1;
+			rec_space_id = 0;
+		} else {
+			rec_page_no = ibuf_rec_get_page_no(mtr, rec);
+			rec_space_id = ibuf_rec_get_space(mtr, rec);
+			/* In the system tablespace the smallest
+			possible secondary index leaf page number is
+			bigger than FSP_DICT_HDR_PAGE_NO (7).
+			In all tablespaces, pages 0 and 1 are reserved
+			for the allocation bitmap and the change
+			buffer bitmap. In file-per-table tablespaces,
+			a file segment inode page will be created at
+			page 2 and the clustered index tree is created
+			at page 3.  So for file-per-table tablespaces,
+			page 4 is the smallest possible secondary
+			index leaf page. CREATE TABLESPACE also initially
+			uses pages 2 and 3 for the first created table,
+			but that table may be dropped, allowing page 2
+			to be reused for a secondary index leaf page.
+			To keep this assertion simple, just
+			make sure the page is >= 2. */
+			ut_ad(rec_page_no >= FSP_FIRST_INODE_PAGE_NO);
+		}
+
+#ifdef UNIV_IBUF_DEBUG
+		ut_a(*n_stored < IBUF_MAX_N_PAGES_MERGED);
+#endif
+		if ((rec_space_id != prev_space_id
+		     || rec_page_no != prev_page_no)
+		    && (prev_space_id != 0 || prev_page_no != 0)) {
+
+			if (contract
+			    || (prev_page_no == first_page_no
+				&& prev_space_id == first_space_id)
+			    || (volume_for_page
+				> ((IBUF_MERGE_THRESHOLD - 1)
+				   * 4U << srv_page_size_shift
+				   / IBUF_PAGE_SIZE_PER_FREE_SPACE)
+				/ IBUF_MERGE_THRESHOLD)) {
+
+				space_ids[*n_stored] = prev_space_id;
+				page_nos[*n_stored] = prev_page_no;
+
+				(*n_stored)++;
+
+				sum_volumes += volume_for_page;
+			}
+
+			if (rec_space_id != first_space_id
+			    || rec_page_no / IBUF_MERGE_AREA
+			    != first_page_no / IBUF_MERGE_AREA) {
+
+				break;
+			}
+
+			volume_for_page = 0;
+		}
+
+		if (rec_page_no == 1 && rec_space_id == 0) {
+			/* Supremum record */
+
+			break;
+		}
+
+		rec_volume = ibuf_rec_get_volume(mtr, rec);
+
+		volume_for_page += rec_volume;
+
+		prev_page_no = rec_page_no;
+		prev_space_id = rec_space_id;
+
+		rec = page_rec_get_next_const(rec);
+	}
+
+#ifdef UNIV_IBUF_DEBUG
+	ut_a(*n_stored <= IBUF_MAX_N_PAGES_MERGED);
+#endif
+#if 0
+	fprintf(stderr, "Ibuf merge batch %lu pages %lu volume\n",
+		*n_stored, sum_volumes);
+#endif
+	return(sum_volumes);
+}
+
+/*******************************************************************//**
+Get the matching records for space id.
+@return current rec or NULL */
+static	MY_ATTRIBUTE((nonnull, warn_unused_result))
+const rec_t*
+ibuf_get_user_rec(
+/*===============*/
+	btr_pcur_t*	pcur,		/*!< in: the current cursor */
+	mtr_t*		mtr)		/*!< in: mini transaction */
+{
+	do {
+		const rec_t* rec = btr_pcur_get_rec(pcur);
+
+		if (page_rec_is_user_rec(rec)) {
+			return(rec);
+		}
+	} while (btr_pcur_move_to_next(pcur, mtr));
+
+	return(NULL);
+}
+
+/*********************************************************************//**
+Reads page numbers for a space id from an ibuf tree.
+@return a lower limit for the combined volume of records which will be
+merged */
+static	MY_ATTRIBUTE((nonnull, warn_unused_result))
+ulint
+ibuf_get_merge_pages(
+/*=================*/
+	btr_pcur_t*	pcur,	/*!< in/out: cursor */
+	uint32_t	space,	/*!< in: space for which to merge */
+	ulint		limit,	/*!< in: max page numbers to read */
+	uint32_t*	pages,	/*!< out: pages read */
+	uint32_t*	spaces,	/*!< out: spaces read */
+	ulint*		n_pages,/*!< out: number of pages read */
+	mtr_t*		mtr)	/*!< in: mini transaction */
+{
+	const rec_t*	rec;
+	ulint		volume = 0;
+
+	*n_pages = 0;
+
+	while ((rec = ibuf_get_user_rec(pcur, mtr)) != 0
+	       && ibuf_rec_get_space(mtr, rec) == space
+	       && *n_pages < limit) {
+
+		uint32_t page_no = ibuf_rec_get_page_no(mtr, rec);
+
+		if (*n_pages == 0 || pages[*n_pages - 1] != page_no) {
+			spaces[*n_pages] = space;
+			pages[*n_pages] = page_no;
+			++*n_pages;
+		}
+
+		volume += ibuf_rec_get_volume(mtr, rec);
+
+		btr_pcur_move_to_next(pcur, mtr);
+	}
+
+	return(volume);
+}
+
+/**
+Delete a change buffer record.
+@param[in]	page_id		page identifier
+@param[in,out]	pcur		persistent cursor positioned on the record
+@param[in]	search_tuple	search key for (space,page_no)
+@param[in,out]	mtr		mini-transaction
+@return whether mtr was committed (due to pessimistic operation) */
+static MY_ATTRIBUTE((warn_unused_result, nonnull))
+bool ibuf_delete_rec(const page_id_t page_id, btr_pcur_t* pcur,
+		     const dtuple_t* search_tuple, mtr_t* mtr);
+
+/** Merge the change buffer to some pages. */
+static void ibuf_read_merge_pages(const uint32_t* space_ids,
+				  const uint32_t* page_nos, ulint n_stored)
+{
+#ifndef DBUG_OFF
+	mem_heap_t* heap = mem_heap_create(512);
+	ulint dops[IBUF_OP_COUNT];
+	memset(dops, 0, sizeof(dops));
+#endif
+
+	for (ulint i = 0; i < n_stored; i++) {
+		const ulint space_id = space_ids[i];
+		fil_space_t* s = fil_space_t::get(space_id);
+		if (!s) {
+tablespace_deleted:
+			/* The tablespace was not found: remove all
+			entries for it */
+			ibuf_delete_for_discarded_space(space_id);
+			while (i + 1 < n_stored
+			       && space_ids[i + 1] == space_id) {
+				i++;
+			}
+			continue;
+		}
+
+		const ulint zip_size = s->zip_size(), size = s->size;
+		s->release();
+		mtr_t mtr;
+
+		if (UNIV_LIKELY(page_nos[i] < size)) {
+			mtr.start();
+			dberr_t err;
+			buf_page_get_gen(page_id_t(space_id, page_nos[i]),
+					 zip_size, RW_X_LATCH, nullptr,
+					 BUF_GET_POSSIBLY_FREED,
+					 __FILE__, __LINE__, &mtr, &err, true);
+			mtr.commit();
+			if (err == DB_TABLESPACE_DELETED) {
+				goto tablespace_deleted;
+			}
+		}
+#ifndef DBUG_OFF
+		DBUG_EXECUTE_IF("ibuf_merge_corruption", goto work_around;);
+		continue;
+
+		/* The following code works around a hang when the
+		change buffer is corrupted, likely due to the race
+		condition in crash recovery that was fixed in
+		MDEV-24449. But, it also introduces corruption by
+		itself in the following scenario:
+
+		(1) We merged buffered changes in buf_page_get_gen()
+		(2) We committed the mini-transaction
+		(3) Redo log and the page with the merged changes is written
+		(4) A write completion callback thread evicts the page.
+		(5) Other threads buffer changes for that page.
+		(6) We will wrongly discard those newly buffered changes below.
+
+		This code will be available in debug builds, so that
+		users may try to fix a shutdown hang that occurs due
+		to a corrupted change buffer. */
+
+work_around:
+		/* Prevent an infinite loop, by removing entries from
+		the change buffer also in the case the bitmap bits were
+		wrongly clear even though buffered changes exist. */
+		const dtuple_t* tuple = ibuf_search_tuple_build(
+			space_id, page_nos[i], heap);
+loop:
+		btr_pcur_t pcur;
+		ibuf_mtr_start(&mtr);
+		btr_pcur_open(ibuf.index, tuple, PAGE_CUR_GE, BTR_MODIFY_LEAF,
+			      &pcur, &mtr);
+		if (!btr_pcur_is_on_user_rec(&pcur)) {
+			ut_ad(btr_pcur_is_after_last_on_page(&pcur));
+			goto done;
+		}
+
+		for (;;) {
+			ut_ad(btr_pcur_is_on_user_rec(&pcur));
+
+			const rec_t* ibuf_rec = btr_pcur_get_rec(&pcur);
+			if (ibuf_rec_get_space(&mtr, ibuf_rec) != space_id
+			    || ibuf_rec_get_page_no(&mtr, ibuf_rec)
+			    != page_nos[i]) {
+				break;
+			}
+
+			dops[ibuf_rec_get_op_type(&mtr, ibuf_rec)]++;
+			/* Delete the record from ibuf */
+			if (ibuf_delete_rec(page_id_t(space_id, page_nos[i]),
+					    &pcur, tuple, &mtr)) {
+				/* Deletion was pessimistic and mtr
+				was committed: we start from the
+				beginning again */
+				ut_ad(mtr.has_committed());
+				goto loop;
+			}
+
+			if (btr_pcur_is_after_last_on_page(&pcur)) {
+				ibuf_mtr_commit(&mtr);
+				btr_pcur_close(&pcur);
+				goto loop;
+			}
+		}
+done:
+		ibuf_mtr_commit(&mtr);
+		btr_pcur_close(&pcur);
+		mem_heap_empty(heap);
+#endif
+	}
+
+#ifndef DBUG_OFF
+	ibuf_add_ops(ibuf.n_discarded_ops, dops);
+	mem_heap_free(heap);
+#endif
+}
+
+/*********************************************************************//**
+Contracts insert buffer trees by reading pages to the buffer pool.
+@return a lower limit for the combined size in bytes of entries which
+will be merged from ibuf trees to the pages read, 0 if ibuf is
+empty */
+static
+ulint
+ibuf_merge_pages(
+/*=============*/
+	ulint*	n_pages)	/*!< out: number of pages to which merged */
+{
+	mtr_t		mtr;
+	btr_pcur_t	pcur;
+	ulint		sum_sizes;
+	uint32_t	page_nos[IBUF_MAX_N_PAGES_MERGED];
+	uint32_t	space_ids[IBUF_MAX_N_PAGES_MERGED];
+
+	*n_pages = 0;
+
+	ibuf_mtr_start(&mtr);
+
+	/* Open a cursor to a randomly chosen leaf of the tree, at a random
+	position within the leaf */
+	bool available;
+
+	available = btr_pcur_open_at_rnd_pos(ibuf.index, BTR_SEARCH_LEAF,
+					     &pcur, &mtr);
+	/* No one should make this index unavailable when server is running */
+	ut_a(available);
+
+	ut_ad(page_validate(btr_pcur_get_page(&pcur), ibuf.index));
+
+	if (page_is_empty(btr_pcur_get_page(&pcur))) {
+		/* If a B-tree page is empty, it must be the root page
+		and the whole B-tree must be empty. InnoDB does not
+		allow empty B-tree pages other than the root. */
+		ut_ad(ibuf.empty);
+		ut_ad(btr_pcur_get_block(&pcur)->page.id()
+		      == page_id_t(IBUF_SPACE_ID, FSP_IBUF_TREE_ROOT_PAGE_NO));
+
+		ibuf_mtr_commit(&mtr);
+		btr_pcur_close(&pcur);
+
+		return(0);
+	}
+
+	sum_sizes = ibuf_get_merge_page_nos(TRUE,
+					    btr_pcur_get_rec(&pcur), &mtr,
+					    space_ids,
+					    page_nos, n_pages);
+	ibuf_mtr_commit(&mtr);
+	btr_pcur_close(&pcur);
+
+	ibuf_read_merge_pages(space_ids, page_nos, *n_pages);
+
+	return(sum_sizes + 1);
+}
+
+/*********************************************************************//**
+Contracts insert buffer trees by reading pages referring to space_id
+to the buffer pool.
+@returns number of pages merged.*/
+ulint
+ibuf_merge_space(
+/*=============*/
+	ulint		space)	/*!< in: tablespace id to merge */
+{
+	mtr_t		mtr;
+	btr_pcur_t	pcur;
+	mem_heap_t*	heap = mem_heap_create(512);
+	dtuple_t*	tuple = ibuf_search_tuple_build(space, 0, heap);
+	ulint		n_pages = 0;
+
+	ut_ad(space < SRV_SPACE_ID_UPPER_BOUND);
+
+	ibuf_mtr_start(&mtr);
+
+	/* Position the cursor on the first matching record. */
+
+	btr_pcur_open(
+		ibuf.index, tuple, PAGE_CUR_GE, BTR_SEARCH_LEAF, &pcur,
+		&mtr);
+
+	mem_heap_free(heap);
+
+	ut_ad(page_validate(btr_pcur_get_page(&pcur), ibuf.index));
+
+	ulint		sum_sizes = 0;
+	uint32_t	pages[IBUF_MAX_N_PAGES_MERGED];
+	uint32_t	spaces[IBUF_MAX_N_PAGES_MERGED];
+
+	if (page_is_empty(btr_pcur_get_page(&pcur))) {
+		/* If a B-tree page is empty, it must be the root page
+		and the whole B-tree must be empty. InnoDB does not
+		allow empty B-tree pages other than the root. */
+		ut_ad(ibuf.empty);
+		ut_ad(btr_pcur_get_block(&pcur)->page.id()
+		      == page_id_t(IBUF_SPACE_ID, FSP_IBUF_TREE_ROOT_PAGE_NO));
+	} else {
+
+		sum_sizes = ibuf_get_merge_pages(
+			&pcur, uint32_t(space), IBUF_MAX_N_PAGES_MERGED,
+			&pages[0], &spaces[0], &n_pages,
+			&mtr);
+		ib::info() << "Size of pages merged " << sum_sizes;
+	}
+
+	ibuf_mtr_commit(&mtr);
+
+	btr_pcur_close(&pcur);
+
+	if (n_pages > 0) {
+		ut_ad(n_pages <= UT_ARR_SIZE(pages));
+
+#ifdef UNIV_DEBUG
+		for (ulint i = 0; i < n_pages; ++i) {
+			ut_ad(spaces[i] == space);
+		}
+#endif /* UNIV_DEBUG */
+
+		ibuf_read_merge_pages(spaces, pages, n_pages);
+	}
+
+	return(n_pages);
+}
+
+/** Contract the change buffer by reading pages to the buffer pool.
+@param[out]	n_pages		number of pages merged
+@param[in]	sync		whether the caller waits for
+the issued reads to complete
+@return a lower limit for the combined size in bytes of entries which
+will be merged from ibuf trees to the pages read, 0 if ibuf is
+empty */
+MY_ATTRIBUTE((warn_unused_result))
+static ulint ibuf_merge(ulint* n_pages)
+{
+	*n_pages = 0;
+
+	/* We perform a dirty read of ibuf.empty, without latching
+	the insert buffer root page. We trust this dirty read except
+	when a slow shutdown is being executed. During a slow
+	shutdown, the insert buffer merge must be completed. */
+
+	if (ibuf.empty && srv_shutdown_state <= SRV_SHUTDOWN_INITIATED) {
+		return(0);
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+	} else if (ibuf_debug) {
+		return(0);
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+	} else {
+		return ibuf_merge_pages(n_pages);
+	}
+}
+
+/** Contract the change buffer by reading pages to the buffer pool.
+@return a lower limit for the combined size in bytes of entries which
+will be merged from ibuf trees to the pages read, 0 if ibuf is empty */
+static ulint ibuf_contract()
+{
+	ulint n_pages;
+	return ibuf_merge_pages(&n_pages);
+}
+
+/** Contract the change buffer by reading pages to the buffer pool.
+@return a lower limit for the combined size in bytes of entries which
+will be merged from ibuf trees to the pages read, 0 if ibuf is
+empty */
+ulint ibuf_merge_all()
+{
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+	if (ibuf_debug) {
+		return(0);
+	}
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
+	ulint	sum_bytes	= 0;
+	ulint	n_pages = srv_io_capacity;
+
+	for (ulint sum_pages = 0; sum_pages < n_pages; ) {
+		ulint n_pag2;
+		ulint n_bytes = ibuf_merge(&n_pag2);
+
+		if (n_bytes == 0) {
+			break;
+		}
+
+		sum_bytes += n_bytes;
+	}
+
+	return sum_bytes;
+}
+
+/*********************************************************************//**
+Contract insert buffer trees after insert if they are too big. */
+UNIV_INLINE
+void
+ibuf_contract_after_insert(
+/*=======================*/
+	ulint	entry_size)	/*!< in: size of a record which was inserted
+				into an ibuf tree */
+{
+	/* Perform dirty reads of ibuf.size and ibuf.max_size, to
+	reduce ibuf_mutex contention. ibuf.max_size remains constant
+	after ibuf_init_at_db_start(), but ibuf.size should be
+	protected by ibuf_mutex. Given that ibuf.size fits in a
+	machine word, this should be OK; at worst we are doing some
+	excessive ibuf_contract() or occasionally skipping a
+	ibuf_contract(). */
+	if (ibuf.size < ibuf.max_size) {
+		return;
+	}
+
+	/* Contract at least entry_size many bytes */
+	ulint sum_sizes = 0;
+	ulint size;
+
+	do {
+		size = ibuf_contract();
+		sum_sizes += size;
+	} while (size > 0 && sum_sizes < entry_size);
+}
+
+/** Determine if a change buffer record has been encountered already.
+@param rec   change buffer record in the MySQL 5.5 format
+@param hash  hash table of encountered records
+@param size  number of elements in hash
+@retval true if a distinct record
+@retval false if this may be duplicating an earlier record */
+static bool ibuf_get_volume_buffered_hash(const rec_t *rec, ulint *hash,
+                                          ulint size)
+{
+  ut_ad(rec_get_n_fields_old(rec) > IBUF_REC_FIELD_USER);
+  const ulint start= rec_get_field_start_offs(rec, IBUF_REC_FIELD_USER);
+  const ulint len= rec_get_data_size_old(rec) - start;
+  const uint32_t fold= ut_crc32(rec + start, len);
+  hash+= (fold / (CHAR_BIT * sizeof *hash)) % size;
+  ulint bitmask= static_cast<ulint>(1) << (fold % (CHAR_BIT * sizeof(*hash)));
+
+  if (*hash & bitmask)
+    return false;
+
+  /* We have not seen this record yet. Remember it. */
+  *hash|= bitmask;
+  return true;
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_get_volume_buffered_count(mtr,rec,hash,size,n_recs)	\
+	ibuf_get_volume_buffered_count_func(mtr,rec,hash,size,n_recs)
+#else /* UNIV_DEBUG */
+# define ibuf_get_volume_buffered_count(mtr,rec,hash,size,n_recs)	\
+	ibuf_get_volume_buffered_count_func(rec,hash,size,n_recs)
+#endif /* UNIV_DEBUG */
+
+/*********************************************************************//**
+Update the estimate of the number of records on a page, and
+get the space taken by merging the buffered record to the index page.
+@return size of index record in bytes + an upper limit of the space
+taken in the page directory */
+static
+ulint
+ibuf_get_volume_buffered_count_func(
+/*================================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,	/*!< in: mini-transaction owning rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	rec,	/*!< in: insert buffer record */
+	ulint*		hash,	/*!< in/out: hash array */
+	ulint		size,	/*!< in: number of elements in hash array */
+	lint*		n_recs)	/*!< in/out: estimated number of records
+				on the page that rec points to */
+{
+	ulint		len;
+	ibuf_op_t	ibuf_op;
+	const byte*	types;
+	ulint		n_fields;
+
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(ibuf_inside(mtr));
+
+	n_fields = rec_get_n_fields_old(rec);
+	ut_ad(n_fields > IBUF_REC_FIELD_USER);
+	n_fields -= IBUF_REC_FIELD_USER;
+
+	rec_get_nth_field_offs_old(rec, 1, &len);
+	/* This function is only invoked when buffering new
+	operations.  All pre-4.1 records should have been merged
+	when the database was started up. */
+	ut_a(len == 1);
+
+	if (rec_get_deleted_flag(rec, 0)) {
+		/* This record has been merged already,
+		but apparently the system crashed before
+		the change was discarded from the buffer.
+		Pretend that the record does not exist. */
+		return(0);
+	}
+
+	types = rec_get_nth_field_old(rec, IBUF_REC_FIELD_METADATA, &len);
+
+	switch (UNIV_EXPECT(int(len % DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE),
+			    IBUF_REC_INFO_SIZE)) {
+	default:
+		ut_error;
+	case 0:
+		/* This ROW_TYPE=REDUNDANT record does not include an
+		operation counter.  Exclude it from the *n_recs,
+		because deletes cannot be buffered if there are
+		old-style inserts buffered for the page. */
+
+		len = ibuf_rec_get_size(rec, types, n_fields, 0);
+
+		return(len
+		       + rec_get_converted_extra_size(len, n_fields, 0)
+		       + page_dir_calc_reserved_space(1));
+	case 1:
+		/* This ROW_TYPE=COMPACT record does not include an
+		operation counter.  Exclude it from the *n_recs,
+		because deletes cannot be buffered if there are
+		old-style inserts buffered for the page. */
+		goto get_volume_comp;
+
+	case IBUF_REC_INFO_SIZE:
+		ibuf_op = (ibuf_op_t) types[IBUF_REC_OFFSET_TYPE];
+		break;
+	}
+
+	switch (ibuf_op) {
+	case IBUF_OP_INSERT:
+		/* Inserts can be done by updating a delete-marked record.
+		Because delete-mark and insert operations can be pointing to
+		the same records, we must not count duplicates. */
+	case IBUF_OP_DELETE_MARK:
+		/* There must be a record to delete-mark.
+		See if this record has been already buffered. */
+		if (n_recs && ibuf_get_volume_buffered_hash(rec, hash, size)) {
+			(*n_recs)++;
+		}
+
+		if (ibuf_op == IBUF_OP_DELETE_MARK) {
+			/* Setting the delete-mark flag does not
+			affect the available space on the page. */
+			return(0);
+		}
+		break;
+	case IBUF_OP_DELETE:
+		/* A record will be removed from the page. */
+		if (n_recs) {
+			(*n_recs)--;
+		}
+		/* While deleting a record actually frees up space,
+		we have to play it safe and pretend that it takes no
+		additional space (the record might not exist, etc.). */
+		return(0);
+	default:
+		ut_error;
+	}
+
+	ut_ad(ibuf_op == IBUF_OP_INSERT);
+
+get_volume_comp:
+	{
+		dtuple_t*	entry;
+		ulint		volume;
+		dict_index_t*	dummy_index;
+		mem_heap_t*	heap = mem_heap_create(500);
+
+		entry = ibuf_build_entry_from_ibuf_rec(
+			mtr, rec, heap, &dummy_index);
+
+		volume = rec_get_converted_size(dummy_index, entry, 0);
+
+		ibuf_dummy_index_free(dummy_index);
+		mem_heap_free(heap);
+
+		return(volume + page_dir_calc_reserved_space(1));
+	}
+}
+
+/*********************************************************************//**
+Gets an upper limit for the combined size of entries buffered in the insert
+buffer for a given page.
+@return upper limit for the volume of buffered inserts for the index
+page, in bytes; srv_page_size, if the entries for the index page span
+several pages in the insert buffer */
+static
+ulint
+ibuf_get_volume_buffered(
+/*=====================*/
+	const btr_pcur_t*pcur,	/*!< in: pcur positioned at a place in an
+				insert buffer tree where we would insert an
+				entry for the index page whose number is
+				page_no, latch mode has to be BTR_MODIFY_PREV
+				or BTR_MODIFY_TREE */
+	ulint		space,	/*!< in: space id */
+	ulint		page_no,/*!< in: page number of an index page */
+	lint*		n_recs,	/*!< in/out: minimum number of records on the
+				page after the buffered changes have been
+				applied, or NULL to disable the counting */
+	mtr_t*		mtr)	/*!< in: mini-transaction of pcur */
+{
+	ulint		volume;
+	const rec_t*	rec;
+	const page_t*	page;
+	const page_t*	prev_page;
+	const page_t*	next_page;
+	/* bitmap of buffered recs */
+	ulint		hash_bitmap[128 / sizeof(ulint)];
+
+	ut_ad((pcur->latch_mode == BTR_MODIFY_PREV)
+	      || (pcur->latch_mode == BTR_MODIFY_TREE));
+
+	/* Count the volume of inserts earlier in the alphabetical order than
+	pcur */
+
+	volume = 0;
+
+	if (n_recs) {
+		memset(hash_bitmap, 0, sizeof hash_bitmap);
+	}
+
+	rec = btr_pcur_get_rec(pcur);
+	page = page_align(rec);
+	ut_ad(page_validate(page, ibuf.index));
+
+	if (page_rec_is_supremum(rec)) {
+		rec = page_rec_get_prev_const(rec);
+	}
+
+	uint32_t prev_page_no;
+
+	for (; !page_rec_is_infimum(rec);
+	     rec = page_rec_get_prev_const(rec)) {
+		ut_ad(page_align(rec) == page);
+
+		if (page_no != ibuf_rec_get_page_no(mtr, rec)
+		    || space != ibuf_rec_get_space(mtr, rec)) {
+
+			goto count_later;
+		}
+
+		volume += ibuf_get_volume_buffered_count(
+			mtr, rec,
+			hash_bitmap, UT_ARR_SIZE(hash_bitmap), n_recs);
+	}
+
+	/* Look at the previous page */
+
+	prev_page_no = btr_page_get_prev(page);
+
+	if (prev_page_no == FIL_NULL) {
+
+		goto count_later;
+	}
+
+	{
+		buf_block_t*	block;
+
+		block = buf_page_get(
+			page_id_t(IBUF_SPACE_ID, prev_page_no),
+			0, RW_X_LATCH, mtr);
+
+		buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE);
+
+		prev_page = buf_block_get_frame(block);
+		ut_ad(page_validate(prev_page, ibuf.index));
+	}
+
+#ifdef UNIV_BTR_DEBUG
+	static_assert(FIL_PAGE_NEXT % 4 == 0, "alignment");
+	static_assert(FIL_PAGE_OFFSET % 4 == 0, "alignment");
+	ut_a(!memcmp_aligned<4>(prev_page + FIL_PAGE_NEXT,
+				page + FIL_PAGE_OFFSET, 4));
+#endif /* UNIV_BTR_DEBUG */
+
+	rec = page_get_supremum_rec(prev_page);
+	rec = page_rec_get_prev_const(rec);
+
+	for (;; rec = page_rec_get_prev_const(rec)) {
+		ut_ad(page_align(rec) == prev_page);
+
+		if (page_rec_is_infimum(rec)) {
+
+			/* We cannot go to yet a previous page, because we
+			do not have the x-latch on it, and cannot acquire one
+			because of the latching order: we have to give up */
+
+			return(srv_page_size);
+		}
+
+		if (page_no != ibuf_rec_get_page_no(mtr, rec)
+		    || space != ibuf_rec_get_space(mtr, rec)) {
+
+			goto count_later;
+		}
+
+		volume += ibuf_get_volume_buffered_count(
+			mtr, rec,
+			hash_bitmap, UT_ARR_SIZE(hash_bitmap), n_recs);
+	}
+
+count_later:
+	rec = btr_pcur_get_rec(pcur);
+
+	if (!page_rec_is_supremum(rec)) {
+		rec = page_rec_get_next_const(rec);
+	}
+
+	for (; !page_rec_is_supremum(rec);
+	     rec = page_rec_get_next_const(rec)) {
+		if (page_no != ibuf_rec_get_page_no(mtr, rec)
+		    || space != ibuf_rec_get_space(mtr, rec)) {
+
+			return(volume);
+		}
+
+		volume += ibuf_get_volume_buffered_count(
+			mtr, rec,
+			hash_bitmap, UT_ARR_SIZE(hash_bitmap), n_recs);
+	}
+
+	/* Look at the next page */
+
+	uint32_t next_page_no = btr_page_get_next(page);
+
+	if (next_page_no == FIL_NULL) {
+
+		return(volume);
+	}
+
+	{
+		buf_block_t*	block;
+
+		block = buf_page_get(
+			page_id_t(IBUF_SPACE_ID, next_page_no),
+			0, RW_X_LATCH, mtr);
+
+		buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE);
+
+		next_page = buf_block_get_frame(block);
+		ut_ad(page_validate(next_page, ibuf.index));
+	}
+
+#ifdef UNIV_BTR_DEBUG
+	static_assert(FIL_PAGE_PREV % 4 == 0, "alignment");
+	static_assert(FIL_PAGE_OFFSET % 4 == 0, "alignment");
+	ut_a(!memcmp_aligned<4>(next_page + FIL_PAGE_PREV,
+				page + FIL_PAGE_OFFSET, 4));
+#endif /* UNIV_BTR_DEBUG */
+
+	rec = page_get_infimum_rec(next_page);
+	rec = page_rec_get_next_const(rec);
+
+	for (;; rec = page_rec_get_next_const(rec)) {
+		ut_ad(page_align(rec) == next_page);
+
+		if (page_rec_is_supremum(rec)) {
+
+			/* We give up */
+
+			return(srv_page_size);
+		}
+
+		if (page_no != ibuf_rec_get_page_no(mtr, rec)
+		    || space != ibuf_rec_get_space(mtr, rec)) {
+
+			return(volume);
+		}
+
+		volume += ibuf_get_volume_buffered_count(
+			mtr, rec,
+			hash_bitmap, UT_ARR_SIZE(hash_bitmap), n_recs);
+	}
+}
+
+/*********************************************************************//**
+Reads the biggest tablespace id from the high end of the insert buffer
+tree and updates the counter in fil_system. */
+void
+ibuf_update_max_tablespace_id(void)
+/*===============================*/
+{
+	ulint		max_space_id;
+	const rec_t*	rec;
+	const byte*	field;
+	ulint		len;
+	btr_pcur_t	pcur;
+	mtr_t		mtr;
+
+	ut_a(!dict_table_is_comp(ibuf.index->table));
+
+	ibuf_mtr_start(&mtr);
+
+	btr_pcur_open_at_index_side(
+		false, ibuf.index, BTR_SEARCH_LEAF, &pcur, true, 0, &mtr);
+
+	ut_ad(page_validate(btr_pcur_get_page(&pcur), ibuf.index));
+
+	btr_pcur_move_to_prev(&pcur, &mtr);
+
+	if (btr_pcur_is_before_first_on_page(&pcur)) {
+		/* The tree is empty */
+
+		max_space_id = 0;
+	} else {
+		rec = btr_pcur_get_rec(&pcur);
+
+		field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_SPACE, &len);
+
+		ut_a(len == 4);
+
+		max_space_id = mach_read_from_4(field);
+	}
+
+	ibuf_mtr_commit(&mtr);
+
+	/* printf("Maximum space id in insert buffer %lu\n", max_space_id); */
+
+	fil_set_max_space_id_if_bigger(max_space_id);
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_get_entry_counter_low(mtr,rec,space,page_no)	\
+	ibuf_get_entry_counter_low_func(mtr,rec,space,page_no)
+#else /* UNIV_DEBUG */
+# define ibuf_get_entry_counter_low(mtr,rec,space,page_no)	\
+	ibuf_get_entry_counter_low_func(rec,space,page_no)
+#endif
+/****************************************************************//**
+Helper function for ibuf_get_entry_counter_func. Checks if rec is for
+(space, page_no), and if so, reads counter value from it and returns
+that + 1.
+@retval ULINT_UNDEFINED if the record does not contain any counter
+@retval 0 if the record is not for (space, page_no)
+@retval 1 + previous counter value, otherwise */
+static
+ulint
+ibuf_get_entry_counter_low_func(
+/*============================*/
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,		/*!< in: mini-transaction of rec */
+#endif /* UNIV_DEBUG */
+	const rec_t*	rec,		/*!< in: insert buffer record */
+	ulint		space,		/*!< in: space id */
+	ulint		page_no)	/*!< in: page number */
+{
+	ulint		counter;
+	const byte*	field;
+	ulint		len;
+
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX
+					      | MTR_MEMO_PAGE_S_FIX));
+	ut_ad(rec_get_n_fields_old(rec) > 2);
+
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_MARKER, &len);
+
+	ut_a(len == 1);
+
+	/* Check the tablespace identifier. */
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_SPACE, &len);
+
+	ut_a(len == 4);
+
+	if (mach_read_from_4(field) != space) {
+
+		return(0);
+	}
+
+	/* Check the page offset. */
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_PAGE, &len);
+	ut_a(len == 4);
+
+	if (mach_read_from_4(field) != page_no) {
+
+		return(0);
+	}
+
+	/* Check if the record contains a counter field. */
+	field = rec_get_nth_field_old(rec, IBUF_REC_FIELD_METADATA, &len);
+
+	switch (len % DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE) {
+	default:
+		ut_error;
+	case 0: /* ROW_FORMAT=REDUNDANT */
+	case 1: /* ROW_FORMAT=COMPACT */
+		return(ULINT_UNDEFINED);
+
+	case IBUF_REC_INFO_SIZE:
+		counter = mach_read_from_2(field + IBUF_REC_OFFSET_COUNTER);
+		ut_a(counter < 0xFFFF);
+		return(counter + 1);
+	}
+}
+
+#ifdef UNIV_DEBUG
+# define ibuf_get_entry_counter(space,page_no,rec,mtr,exact_leaf) \
+	ibuf_get_entry_counter_func(space,page_no,rec,mtr,exact_leaf)
+#else /* UNIV_DEBUG */
+# define ibuf_get_entry_counter(space,page_no,rec,mtr,exact_leaf) \
+	ibuf_get_entry_counter_func(space,page_no,rec,exact_leaf)
+#endif /* UNIV_DEBUG */
+
+/****************************************************************//**
+Calculate the counter field for an entry based on the current
+last record in ibuf for (space, page_no).
+@return the counter field, or ULINT_UNDEFINED
+if we should abort this insertion to ibuf */
+static
+ulint
+ibuf_get_entry_counter_func(
+/*========================*/
+	ulint		space,		/*!< in: space id of entry */
+	ulint		page_no,	/*!< in: page number of entry */
+	const rec_t*	rec,		/*!< in: the record preceding the
+					insertion point */
+#ifdef UNIV_DEBUG
+	mtr_t*		mtr,		/*!< in: mini-transaction */
+#endif /* UNIV_DEBUG */
+	ibool		only_leaf)	/*!< in: TRUE if this is the only
+					leaf page that can contain entries
+					for (space,page_no), that is, there
+					was no exact match for (space,page_no)
+					in the node pointer */
+{
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(mtr->memo_contains_page_flagged(rec, MTR_MEMO_PAGE_X_FIX));
+	ut_ad(page_validate(page_align(rec), ibuf.index));
+
+	if (page_rec_is_supremum(rec)) {
+		/* This is just for safety. The record should be a
+		page infimum or a user record. */
+		ut_ad(0);
+		return(ULINT_UNDEFINED);
+	} else if (!page_rec_is_infimum(rec)) {
+		return(ibuf_get_entry_counter_low(mtr, rec, space, page_no));
+	} else if (only_leaf || !page_has_prev(page_align(rec))) {
+		/* The parent node pointer did not contain the
+		searched for (space, page_no), which means that the
+		search ended on the correct page regardless of the
+		counter value, and since we're at the infimum record,
+		there are no existing records. */
+		return(0);
+	} else {
+		/* We used to read the previous page here. It would
+		break the latching order, because the caller has
+		buffer-fixed an insert buffer bitmap page. */
+		return(ULINT_UNDEFINED);
+	}
+}
+
+
+/** Translates the ibuf free bits to the free space on a page in bytes.
+@param[in]	physical_size	page_size
+@param[in]	bits		value for ibuf bitmap bits
+@return maximum insert size after reorganize for the page */
+inline ulint
+ibuf_index_page_calc_free_from_bits(ulint physical_size, ulint bits)
+{
+	ut_ad(bits < 4);
+	ut_ad(physical_size > IBUF_PAGE_SIZE_PER_FREE_SPACE);
+
+	if (bits == 3) {
+		bits = 4;
+	}
+
+	return bits * physical_size / IBUF_PAGE_SIZE_PER_FREE_SPACE;
+}
+
+/** Buffer an operation in the insert/delete buffer, instead of doing it
+directly to the disk page, if this is possible.
+@param[in]	mode		BTR_MODIFY_PREV or BTR_MODIFY_TREE
+@param[in]	op		operation type
+@param[in]	no_counter	TRUE=use 5.0.3 format; FALSE=allow delete
+buffering
+@param[in]	entry		index entry to insert
+@param[in]	entry_size	rec_get_converted_size(index, entry)
+@param[in,out]	index		index where to insert; must not be unique
+or clustered
+@param[in]	page_id		page id where to insert
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in,out]	thr		query thread
+@return DB_SUCCESS, DB_STRONG_FAIL or other error */
+static MY_ATTRIBUTE((warn_unused_result))
+dberr_t
+ibuf_insert_low(
+	ulint			mode,
+	ibuf_op_t		op,
+	ibool			no_counter,
+	const dtuple_t*		entry,
+	ulint			entry_size,
+	dict_index_t*		index,
+	const page_id_t		page_id,
+	ulint			zip_size,
+	que_thr_t*		thr)
+{
+	big_rec_t*	dummy_big_rec;
+	btr_pcur_t	pcur;
+	btr_cur_t*	cursor;
+	dtuple_t*	ibuf_entry;
+	mem_heap_t*	offsets_heap	= NULL;
+	mem_heap_t*	heap;
+	rec_offs*	offsets		= NULL;
+	ulint		buffered;
+	lint		min_n_recs;
+	rec_t*		ins_rec;
+	buf_block_t*	bitmap_page;
+	buf_block_t*	block;
+	page_t*		root;
+	dberr_t		err;
+	ibool		do_merge;
+	uint32_t	space_ids[IBUF_MAX_N_PAGES_MERGED];
+	uint32_t	page_nos[IBUF_MAX_N_PAGES_MERGED];
+	ulint		n_stored;
+	mtr_t		mtr;
+	mtr_t		bitmap_mtr;
+
+	ut_a(!dict_index_is_clust(index));
+	ut_ad(!dict_index_is_spatial(index));
+	ut_ad(dtuple_check_typed(entry));
+	ut_ad(!no_counter || op == IBUF_OP_INSERT);
+	ut_ad(page_id.space() == index->table->space_id);
+	ut_a(op < IBUF_OP_COUNT);
+
+	do_merge = FALSE;
+
+	/* Perform dirty reads of ibuf.size and ibuf.max_size, to
+	reduce ibuf_mutex contention. Given that ibuf.max_size and
+	ibuf.size fit in a machine word, this should be OK; at worst
+	we are doing some excessive ibuf_contract() or occasionally
+	skipping an ibuf_contract(). */
+	if (ibuf.max_size == 0) {
+		return(DB_STRONG_FAIL);
+	}
+
+	if (ibuf.size >= ibuf.max_size + IBUF_CONTRACT_DO_NOT_INSERT) {
+		/* Insert buffer is now too big, contract it but do not try
+		to insert */
+
+
+#ifdef UNIV_IBUF_DEBUG
+		fputs("Ibuf too big\n", stderr);
+#endif
+		ibuf_contract();
+
+		return(DB_STRONG_FAIL);
+	}
+
+	heap = mem_heap_create(1024);
+
+	/* Build the entry which contains the space id and the page number
+	as the first fields and the type information for other fields, and
+	which will be inserted to the insert buffer. Using a counter value
+	of 0xFFFF we find the last record for (space, page_no), from which
+	we can then read the counter value N and use N + 1 in the record we
+	insert. (We patch the ibuf_entry's counter field to the correct
+	value just before actually inserting the entry.) */
+
+	ibuf_entry = ibuf_entry_build(
+		op, index, entry, page_id.space(), page_id.page_no(),
+		no_counter ? ULINT_UNDEFINED : 0xFFFF, heap);
+
+	/* Open a cursor to the insert buffer tree to calculate if we can add
+	the new entry to it without exceeding the free space limit for the
+	page. */
+
+	if (BTR_LATCH_MODE_WITHOUT_INTENTION(mode) == BTR_MODIFY_TREE) {
+		for (;;) {
+			mutex_enter(&ibuf_pessimistic_insert_mutex);
+			mutex_enter(&ibuf_mutex);
+
+			if (UNIV_LIKELY(ibuf_data_enough_free_for_insert())) {
+
+				break;
+			}
+
+			mutex_exit(&ibuf_mutex);
+			mutex_exit(&ibuf_pessimistic_insert_mutex);
+
+			if (!ibuf_add_free_page()) {
+
+				mem_heap_free(heap);
+				return(DB_STRONG_FAIL);
+			}
+		}
+	}
+
+	ibuf_mtr_start(&mtr);
+
+	btr_pcur_open(ibuf.index, ibuf_entry, PAGE_CUR_LE, mode, &pcur, &mtr);
+	ut_ad(page_validate(btr_pcur_get_page(&pcur), ibuf.index));
+
+	/* Find out the volume of already buffered inserts for the same index
+	page */
+	min_n_recs = 0;
+	buffered = ibuf_get_volume_buffered(&pcur,
+					    page_id.space(),
+					    page_id.page_no(),
+					    op == IBUF_OP_DELETE
+					    ? &min_n_recs
+					    : NULL, &mtr);
+
+	const ulint physical_size = zip_size ? zip_size : srv_page_size;
+
+	if (op == IBUF_OP_DELETE
+	    && (min_n_recs < 2 || buf_pool.watch_occurred(page_id))) {
+		/* The page could become empty after the record is
+		deleted, or the page has been read in to the buffer
+		pool.  Refuse to buffer the operation. */
+
+		/* The buffer pool watch is needed for IBUF_OP_DELETE
+		because of latching order considerations.  We can
+		check buf_pool_watch_occurred() only after latching
+		the insert buffer B-tree pages that contain buffered
+		changes for the page.  We never buffer IBUF_OP_DELETE,
+		unless some IBUF_OP_INSERT or IBUF_OP_DELETE_MARK have
+		been previously buffered for the page.  Because there
+		are buffered operations for the page, the insert
+		buffer B-tree page latches held by mtr will guarantee
+		that no changes for the user page will be merged
+		before mtr_commit(&mtr).  We must not mtr_commit(&mtr)
+		until after the IBUF_OP_DELETE has been buffered. */
+
+fail_exit:
+		if (BTR_LATCH_MODE_WITHOUT_INTENTION(mode) == BTR_MODIFY_TREE) {
+			mutex_exit(&ibuf_mutex);
+			mutex_exit(&ibuf_pessimistic_insert_mutex);
+		}
+
+		err = DB_STRONG_FAIL;
+		goto func_exit;
+	}
+
+	/* After this point, the page could still be loaded to the
+	buffer pool, but we do not have to care about it, since we are
+	holding a latch on the insert buffer leaf page that contains
+	buffered changes for (space, page_no).  If the page enters the
+	buffer pool, buf_page_read_complete() for (space, page_no) will
+	have to acquire a latch on the same insert buffer leaf page,
+	which it cannot do until we have buffered the IBUF_OP_DELETE
+	and done mtr_commit(&mtr) to release the latch. */
+
+	ibuf_mtr_start(&bitmap_mtr);
+
+	bitmap_page = ibuf_bitmap_get_map_page(page_id, zip_size, &bitmap_mtr);
+
+	/* We check if the index page is suitable for buffered entries */
+
+	if (buf_pool.page_hash_contains(page_id)) {
+commit_exit:
+		ibuf_mtr_commit(&bitmap_mtr);
+		goto fail_exit;
+	} else {
+		lock_mutex_enter();
+		const auto lock_exists = lock_sys.get_first(page_id);
+		lock_mutex_exit();
+		if (lock_exists) {
+			goto commit_exit;
+		}
+	}
+
+	if (op == IBUF_OP_INSERT) {
+		ulint	bits = ibuf_bitmap_page_get_bits(
+			bitmap_page->frame, page_id, physical_size,
+			IBUF_BITMAP_FREE, &bitmap_mtr);
+
+		if (buffered + entry_size + page_dir_calc_reserved_space(1)
+		    > ibuf_index_page_calc_free_from_bits(physical_size,
+							  bits)) {
+			/* Release the bitmap page latch early. */
+			ibuf_mtr_commit(&bitmap_mtr);
+
+			/* It may not fit */
+			do_merge = TRUE;
+
+			ibuf_get_merge_page_nos(FALSE,
+						btr_pcur_get_rec(&pcur), &mtr,
+						space_ids,
+						page_nos, &n_stored);
+
+			goto fail_exit;
+		}
+	}
+
+	if (!no_counter) {
+		/* Patch correct counter value to the entry to
+		insert. This can change the insert position, which can
+		result in the need to abort in some cases. */
+		ulint		counter = ibuf_get_entry_counter(
+			page_id.space(), page_id.page_no(),
+			btr_pcur_get_rec(&pcur), &mtr,
+			btr_pcur_get_btr_cur(&pcur)->low_match
+			< IBUF_REC_FIELD_METADATA);
+		dfield_t*	field;
+
+		if (counter == ULINT_UNDEFINED) {
+			goto commit_exit;
+		}
+
+		field = dtuple_get_nth_field(
+			ibuf_entry, IBUF_REC_FIELD_METADATA);
+		mach_write_to_2(
+			(byte*) dfield_get_data(field)
+			+ IBUF_REC_OFFSET_COUNTER, counter);
+	}
+
+	/* Set the bitmap bit denoting that the insert buffer contains
+	buffered entries for this index page, if the bit is not set yet */
+	index->set_modified(bitmap_mtr);
+	ibuf_bitmap_page_set_bits<IBUF_BITMAP_BUFFERED>(
+		bitmap_page, page_id, physical_size, true, &bitmap_mtr);
+	ibuf_mtr_commit(&bitmap_mtr);
+
+	cursor = btr_pcur_get_btr_cur(&pcur);
+
+	if (mode == BTR_MODIFY_PREV) {
+		err = btr_cur_optimistic_insert(
+			BTR_NO_LOCKING_FLAG | BTR_NO_UNDO_LOG_FLAG,
+			cursor, &offsets, &offsets_heap,
+			ibuf_entry, &ins_rec,
+			&dummy_big_rec, 0, thr, &mtr);
+		block = btr_cur_get_block(cursor);
+		ut_ad(block->page.id().space() == IBUF_SPACE_ID);
+
+		/* If this is the root page, update ibuf.empty. */
+		if (block->page.id().page_no() == FSP_IBUF_TREE_ROOT_PAGE_NO) {
+			const page_t*	root = buf_block_get_frame(block);
+
+			ut_ad(page_get_space_id(root) == IBUF_SPACE_ID);
+			ut_ad(page_get_page_no(root)
+			      == FSP_IBUF_TREE_ROOT_PAGE_NO);
+
+			ibuf.empty = page_is_empty(root);
+		}
+	} else {
+		ut_ad(BTR_LATCH_MODE_WITHOUT_INTENTION(mode)
+		      == BTR_MODIFY_TREE);
+
+		/* We acquire an sx-latch to the root page before the insert,
+		because a pessimistic insert releases the tree x-latch,
+		which would cause the sx-latching of the root after that to
+		break the latching order. */
+
+		root = ibuf_tree_root_get(&mtr)->frame;
+
+		err = btr_cur_optimistic_insert(
+			BTR_NO_LOCKING_FLAG | BTR_NO_UNDO_LOG_FLAG,
+			cursor, &offsets, &offsets_heap,
+			ibuf_entry, &ins_rec,
+			&dummy_big_rec, 0, thr, &mtr);
+
+		if (err == DB_FAIL) {
+			err = btr_cur_pessimistic_insert(
+				BTR_NO_LOCKING_FLAG | BTR_NO_UNDO_LOG_FLAG,
+				cursor, &offsets, &offsets_heap,
+				ibuf_entry, &ins_rec,
+				&dummy_big_rec, 0, thr, &mtr);
+		}
+
+		mutex_exit(&ibuf_pessimistic_insert_mutex);
+		ibuf_size_update(root);
+		mutex_exit(&ibuf_mutex);
+		ibuf.empty = page_is_empty(root);
+
+		block = btr_cur_get_block(cursor);
+		ut_ad(block->page.id().space() == IBUF_SPACE_ID);
+	}
+
+	if (offsets_heap) {
+		mem_heap_free(offsets_heap);
+	}
+
+	if (err == DB_SUCCESS && op != IBUF_OP_DELETE) {
+		/* Update the page max trx id field */
+		page_update_max_trx_id(block, NULL,
+				       thr_get_trx(thr)->id, &mtr);
+	}
+
+func_exit:
+	ibuf_mtr_commit(&mtr);
+	btr_pcur_close(&pcur);
+
+	mem_heap_free(heap);
+
+	if (err == DB_SUCCESS
+	    && BTR_LATCH_MODE_WITHOUT_INTENTION(mode) == BTR_MODIFY_TREE) {
+		ibuf_contract_after_insert(entry_size);
+	}
+
+	if (do_merge) {
+#ifdef UNIV_IBUF_DEBUG
+		ut_a(n_stored <= IBUF_MAX_N_PAGES_MERGED);
+#endif
+		ibuf_read_merge_pages(space_ids, page_nos, n_stored);
+	}
+
+	return(err);
+}
+
+/** Buffer an operation in the change buffer, instead of applying it
+directly to the file page, if this is possible. Does not do it if the index
+is clustered or unique.
+@param[in]	op		operation type
+@param[in]	entry		index entry to insert
+@param[in,out]	index		index where to insert
+@param[in]	page_id		page id where to insert
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@param[in,out]	thr		query thread
+@return true if success */
+bool
+ibuf_insert(
+	ibuf_op_t		op,
+	const dtuple_t*		entry,
+	dict_index_t*		index,
+	const page_id_t		page_id,
+	ulint			zip_size,
+	que_thr_t*		thr)
+{
+	dberr_t		err;
+	ulint		entry_size;
+	ibool		no_counter;
+	/* Read the settable global variable only once in
+	this function, so that we will have a consistent view of it. */
+	ibuf_use_t	use		= ibuf_use_t(innodb_change_buffering);
+	DBUG_ENTER("ibuf_insert");
+
+	DBUG_PRINT("ibuf", ("op: %d, space: " UINT32PF ", page_no: " UINT32PF,
+			    op, page_id.space(), page_id.page_no()));
+
+	ut_ad(dtuple_check_typed(entry));
+	ut_ad(page_id.space() != SRV_TMP_SPACE_ID);
+
+	ut_a(!dict_index_is_clust(index));
+	ut_ad(!index->table->is_temporary());
+
+	no_counter = use <= IBUF_USE_INSERT;
+
+	switch (op) {
+	case IBUF_OP_INSERT:
+		switch (use) {
+		case IBUF_USE_NONE:
+		case IBUF_USE_DELETE:
+		case IBUF_USE_DELETE_MARK:
+			DBUG_RETURN(false);
+		case IBUF_USE_INSERT:
+		case IBUF_USE_INSERT_DELETE_MARK:
+		case IBUF_USE_ALL:
+			goto check_watch;
+		}
+		break;
+	case IBUF_OP_DELETE_MARK:
+		switch (use) {
+		case IBUF_USE_NONE:
+		case IBUF_USE_INSERT:
+			DBUG_RETURN(false);
+		case IBUF_USE_DELETE_MARK:
+		case IBUF_USE_DELETE:
+		case IBUF_USE_INSERT_DELETE_MARK:
+		case IBUF_USE_ALL:
+			ut_ad(!no_counter);
+			goto check_watch;
+		}
+		break;
+	case IBUF_OP_DELETE:
+		switch (use) {
+		case IBUF_USE_NONE:
+		case IBUF_USE_INSERT:
+		case IBUF_USE_INSERT_DELETE_MARK:
+			DBUG_RETURN(false);
+		case IBUF_USE_DELETE_MARK:
+		case IBUF_USE_DELETE:
+		case IBUF_USE_ALL:
+			ut_ad(!no_counter);
+			goto skip_watch;
+		}
+		break;
+	case IBUF_OP_COUNT:
+		break;
+	}
+
+	/* unknown op or use */
+	ut_error;
+
+check_watch:
+	/* If a thread attempts to buffer an insert on a page while a
+	purge is in progress on the same page, the purge must not be
+	buffered, because it could remove a record that was
+	re-inserted later.  For simplicity, we block the buffering of
+	all operations on a page that has a purge pending.
+
+	We do not check this in the IBUF_OP_DELETE case, because that
+	would always trigger the buffer pool watch during purge and
+	thus prevent the buffering of delete operations.  We assume
+	that the issuer of IBUF_OP_DELETE has called
+	buf_pool_t::watch_set(). */
+
+	if (buf_pool.page_hash_contains<true>(page_id)) {
+		/* A buffer pool watch has been set or the
+		page has been read into the buffer pool.
+		Do not buffer the request.  If a purge operation
+		is being buffered, have this request executed
+		directly on the page in the buffer pool after the
+		buffered entries for this page have been merged. */
+		DBUG_RETURN(false);
+	}
+
+skip_watch:
+	entry_size = rec_get_converted_size(index, entry, 0);
+
+	if (entry_size
+	    >= page_get_free_space_of_empty(dict_table_is_comp(index->table))
+	    / 2) {
+
+		DBUG_RETURN(false);
+	}
+
+	err = ibuf_insert_low(BTR_MODIFY_PREV, op, no_counter,
+			      entry, entry_size,
+			      index, page_id, zip_size, thr);
+	if (err == DB_FAIL) {
+		err = ibuf_insert_low(BTR_MODIFY_TREE | BTR_LATCH_FOR_INSERT,
+				      op, no_counter, entry, entry_size,
+				      index, page_id, zip_size, thr);
+	}
+
+	ut_a(err == DB_SUCCESS || err == DB_STRONG_FAIL
+	     || err == DB_TOO_BIG_RECORD);
+
+	DBUG_RETURN(err == DB_SUCCESS);
+}
+
+/********************************************************************//**
+During merge, inserts to an index page a secondary index entry extracted
+from the insert buffer.
+@return	newly inserted record */
+static MY_ATTRIBUTE((nonnull))
+rec_t*
+ibuf_insert_to_index_page_low(
+/*==========================*/
+	const dtuple_t*	entry,	/*!< in: buffered entry to insert */
+	buf_block_t*	block,	/*!< in/out: index page where the buffered
+				entry should be placed */
+	dict_index_t*	index,	/*!< in: record descriptor */
+	rec_offs**	offsets,/*!< out: offsets on *rec */
+	mem_heap_t*	heap,	/*!< in/out: memory heap */
+	mtr_t*		mtr,	/*!< in/out: mtr */
+	page_cur_t*	page_cur)/*!< in/out: cursor positioned on the record
+				after which to insert the buffered entry */
+{
+	rec_t*		rec;
+	DBUG_ENTER("ibuf_insert_to_index_page_low");
+
+	rec = page_cur_tuple_insert(page_cur, entry, index,
+				    offsets, &heap, 0, mtr);
+	if (rec != NULL) {
+		DBUG_RETURN(rec);
+	}
+
+	/* Page reorganization or recompression should already have
+	been attempted by page_cur_tuple_insert(). Besides, per
+	ibuf_index_page_calc_free_zip() the page should not have been
+	recompressed or reorganized. */
+	ut_ad(!is_buf_block_get_page_zip(block));
+
+	/* If the record did not fit, reorganize */
+
+	btr_page_reorganize(page_cur, index, mtr);
+
+	/* This time the record must fit */
+
+	rec = page_cur_tuple_insert(page_cur, entry, index,
+				    offsets, &heap, 0, mtr);
+	if (rec != NULL) {
+		DBUG_RETURN(rec);
+	}
+
+	ib::error() << "Insert buffer insert fails; page free "
+		    << page_get_max_insert_size(block->frame, 1)
+		    << ", dtuple size "
+		    << rec_get_converted_size(index, entry, 0);
+
+	fputs("InnoDB: Cannot insert index record ", stderr);
+	dtuple_print(stderr, entry);
+	fputs("\nInnoDB: The table where this index record belongs\n"
+	      "InnoDB: is now probably corrupt. Please run CHECK TABLE on\n"
+	      "InnoDB: that table.\n", stderr);
+
+	if (buf_block_t *bitmap_page =  ibuf_bitmap_get_map_page(
+			block->page.id(), block->zip_size(), mtr)) {
+
+		ib::error() << "page " << block->page.id() << ", size "
+			    << block->physical_size() << ", bitmap bits "
+			    << ibuf_bitmap_page_get_bits(bitmap_page->frame,
+					block->page.id(), block->zip_size(),
+					IBUF_BITMAP_FREE, mtr);
+	}
+
+	ib::error() << BUG_REPORT_MSG;
+
+	ut_ad(0);
+	DBUG_RETURN(NULL);
+}
+
+/************************************************************************
+During merge, inserts to an index page a secondary index entry extracted
+from the insert buffer. */
+static
+void
+ibuf_insert_to_index_page(
+/*======================*/
+	const dtuple_t*	entry,	/*!< in: buffered entry to insert */
+	buf_block_t*	block,	/*!< in/out: index page where the buffered entry
+				should be placed */
+	dict_index_t*	index,	/*!< in: record descriptor */
+	mtr_t*		mtr)	/*!< in: mtr */
+{
+	page_cur_t	page_cur;
+	ulint		low_match;
+	page_t*		page		= buf_block_get_frame(block);
+	rec_t*		rec;
+	rec_offs*	offsets;
+	mem_heap_t*	heap;
+
+	DBUG_ENTER("ibuf_insert_to_index_page");
+
+	DBUG_PRINT("ibuf", ("page " UINT32PF ":" UINT32PF,
+			    block->page.id().space(),
+			    block->page.id().page_no()));
+
+	ut_ad(!dict_index_is_online_ddl(index));// this is an ibuf_dummy index
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(dtuple_check_typed(entry));
+#ifdef BTR_CUR_HASH_ADAPT
+	/* A change buffer merge must occur before users are granted
+	any access to the page. No adaptive hash index entries may
+	point to a freshly read page. */
+	ut_ad(!block->index);
+	assert_block_ahi_empty(block);
+#endif /* BTR_CUR_HASH_ADAPT */
+	ut_ad(mtr->is_named_space(block->page.id().space()));
+
+	if (UNIV_UNLIKELY(dict_table_is_comp(index->table)
+			  != (ibool)!!page_is_comp(page))) {
+		ib::warn() << "Trying to insert a record from the insert"
+			" buffer to an index page but the 'compact' flag does"
+			" not match!";
+		goto dump;
+	}
+
+	rec = page_rec_get_next(page_get_infimum_rec(page));
+
+	if (page_rec_is_supremum(rec)) {
+		ib::warn() << "Trying to insert a record from the insert"
+			" buffer to an index page but the index page"
+			" is empty!";
+		goto dump;
+	}
+
+	if (!rec_n_fields_is_sane(index, rec, entry)) {
+		ib::warn() << "Trying to insert a record from the insert"
+			" buffer to an index page but the number of fields"
+			" does not match!";
+		rec_print(stderr, rec, index);
+dump:
+		dtuple_print(stderr, entry);
+		ut_ad(0);
+
+		ib::warn() << "The table where this index record belongs"
+			" is now probably corrupt. Please run CHECK TABLE on"
+			" your tables. " << BUG_REPORT_MSG;
+
+		DBUG_VOID_RETURN;
+	}
+
+	low_match = page_cur_search(block, index, entry, &page_cur);
+
+	heap = mem_heap_create(
+		sizeof(upd_t)
+		+ REC_OFFS_HEADER_SIZE * sizeof(*offsets)
+		+ dtuple_get_n_fields(entry)
+		* (sizeof(upd_field_t) + sizeof *offsets));
+
+	if (UNIV_UNLIKELY(low_match == dtuple_get_n_fields(entry))) {
+		upd_t*		update;
+
+		rec = page_cur_get_rec(&page_cur);
+
+		/* This is based on
+		row_ins_sec_index_entry_by_modify(BTR_MODIFY_LEAF). */
+		ut_ad(rec_get_deleted_flag(rec, page_is_comp(page)));
+
+		offsets = rec_get_offsets(rec, index, NULL, index->n_fields,
+					  ULINT_UNDEFINED, &heap);
+		update = row_upd_build_sec_rec_difference_binary(
+			rec, index, offsets, entry, heap);
+
+		if (update->n_fields == 0) {
+			/* The records only differ in the delete-mark.
+			Clear the delete-mark, like we did before
+			Bug #56680 was fixed. */
+			btr_rec_set_deleted<false>(block, rec, mtr);
+			goto updated_in_place;
+		}
+
+		/* Copy the info bits. Clear the delete-mark. */
+		update->info_bits = rec_get_info_bits(rec, page_is_comp(page));
+		update->info_bits &= byte(~REC_INFO_DELETED_FLAG);
+		page_zip_des_t* page_zip = buf_block_get_page_zip(block);
+
+		/* We cannot invoke btr_cur_optimistic_update() here,
+		because we do not have a btr_cur_t or que_thr_t,
+		as the insert buffer merge occurs at a very low level. */
+		if (!row_upd_changes_field_size_or_external(index, offsets,
+							    update)
+		    && (!page_zip || btr_cur_update_alloc_zip(
+				page_zip, &page_cur, index, offsets,
+				rec_offs_size(offsets), false, mtr))) {
+			/* This is the easy case. Do something similar
+			to btr_cur_update_in_place(). */
+			rec = page_cur_get_rec(&page_cur);
+			btr_cur_upd_rec_in_place(rec, index, offsets,
+						 update, block, mtr);
+
+			DBUG_EXECUTE_IF(
+				"crash_after_log_ibuf_upd_inplace",
+				log_buffer_flush_to_disk();
+				ib::info() << "Wrote log record for ibuf"
+					" update in place operation";
+				DBUG_SUICIDE();
+			);
+
+			goto updated_in_place;
+		}
+
+		/* btr_cur_update_alloc_zip() may have changed this */
+		rec = page_cur_get_rec(&page_cur);
+
+		/* A collation may identify values that differ in
+		storage length.
+		Some examples (1 or 2 bytes):
+		utf8_turkish_ci: I = U+0131 LATIN SMALL LETTER DOTLESS I
+		utf8_general_ci: S = U+00DF LATIN SMALL LETTER SHARP S
+		utf8_general_ci: A = U+00E4 LATIN SMALL LETTER A WITH DIAERESIS
+
+		latin1_german2_ci: SS = U+00DF LATIN SMALL LETTER SHARP S
+
+		Examples of a character (3-byte UTF-8 sequence)
+		identified with 2 or 4 characters (1-byte UTF-8 sequences):
+
+		utf8_unicode_ci: 'II' = U+2171 SMALL ROMAN NUMERAL TWO
+		utf8_unicode_ci: '(10)' = U+247D PARENTHESIZED NUMBER TEN
+		*/
+
+		/* Delete the different-length record, and insert the
+		buffered one. */
+
+		lock_rec_store_on_page_infimum(block, rec);
+		page_cur_delete_rec(&page_cur, index, offsets, mtr);
+		page_cur_move_to_prev(&page_cur);
+		rec = ibuf_insert_to_index_page_low(entry, block, index,
+				      		    &offsets, heap, mtr,
+						    &page_cur);
+
+		ut_ad(!cmp_dtuple_rec(entry, rec, offsets));
+		lock_rec_restore_from_page_infimum(block, rec, block);
+	} else {
+		offsets = NULL;
+		ibuf_insert_to_index_page_low(entry, block, index,
+					      &offsets, heap, mtr,
+					      &page_cur);
+	}
+updated_in_place:
+	mem_heap_free(heap);
+
+	DBUG_VOID_RETURN;
+}
+
+/****************************************************************//**
+During merge, sets the delete mark on a record for a secondary index
+entry. */
+static
+void
+ibuf_set_del_mark(
+/*==============*/
+	const dtuple_t*		entry,	/*!< in: entry */
+	buf_block_t*		block,	/*!< in/out: block */
+	const dict_index_t*	index,	/*!< in: record descriptor */
+	mtr_t*			mtr)	/*!< in: mtr */
+{
+	page_cur_t	page_cur;
+	ulint		low_match;
+
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(dtuple_check_typed(entry));
+
+	low_match = page_cur_search(block, index, entry, &page_cur);
+
+	if (low_match == dtuple_get_n_fields(entry)) {
+		rec_t* rec = page_cur_get_rec(&page_cur);
+
+		/* Delete mark the old index record. According to a
+		comment in row_upd_sec_index_entry(), it can already
+		have been delete marked if a lock wait occurred in
+		row_ins_sec_index_entry() in a previous invocation of
+		row_upd_sec_index_entry(). */
+
+		if (UNIV_LIKELY
+		    (!rec_get_deleted_flag(
+			    rec, dict_table_is_comp(index->table)))) {
+			btr_rec_set_deleted<true>(block, rec, mtr);
+		}
+	} else {
+		const page_t*		page
+			= page_cur_get_page(&page_cur);
+		const buf_block_t*	block
+			= page_cur_get_block(&page_cur);
+
+		ib::error() << "Unable to find a record to delete-mark";
+		fputs("InnoDB: tuple ", stderr);
+		dtuple_print(stderr, entry);
+		fputs("\n"
+		      "InnoDB: record ", stderr);
+		rec_print(stderr, page_cur_get_rec(&page_cur), index);
+
+		ib::error() << "page " << block->page.id() << " ("
+			<< page_get_n_recs(page) << " records, index id "
+			<< btr_page_get_index_id(page) << ").";
+
+		ib::error() << BUG_REPORT_MSG;
+		ut_ad(0);
+	}
+}
+
+/****************************************************************//**
+During merge, delete a record for a secondary index entry. */
+static
+void
+ibuf_delete(
+/*========*/
+	const dtuple_t*	entry,	/*!< in: entry */
+	buf_block_t*	block,	/*!< in/out: block */
+	dict_index_t*	index,	/*!< in: record descriptor */
+	mtr_t*		mtr)	/*!< in/out: mtr; must be committed
+				before latching any further pages */
+{
+	page_cur_t	page_cur;
+	ulint		low_match;
+
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(dtuple_check_typed(entry));
+	ut_ad(!index->is_spatial());
+	ut_ad(!index->is_clust());
+
+	low_match = page_cur_search(block, index, entry, &page_cur);
+
+	if (low_match == dtuple_get_n_fields(entry)) {
+		page_zip_des_t*	page_zip= buf_block_get_page_zip(block);
+		page_t*		page	= buf_block_get_frame(block);
+		rec_t*		rec	= page_cur_get_rec(&page_cur);
+
+		/* TODO: the below should probably be a separate function,
+		it's a bastardized version of btr_cur_optimistic_delete. */
+
+		rec_offs	offsets_[REC_OFFS_NORMAL_SIZE];
+		rec_offs*	offsets	= offsets_;
+		mem_heap_t*	heap = NULL;
+		ulint		max_ins_size = 0;
+
+		rec_offs_init(offsets_);
+
+		offsets = rec_get_offsets(rec, index, offsets, index->n_fields,
+					  ULINT_UNDEFINED, &heap);
+
+		if (page_get_n_recs(page) <= 1
+		    || !(REC_INFO_DELETED_FLAG
+			 & rec_get_info_bits(rec, page_is_comp(page)))) {
+			/* Refuse to purge the last record or a
+			record that has not been marked for deletion. */
+			ib::error() << "Unable to purge a record";
+			fputs("InnoDB: tuple ", stderr);
+			dtuple_print(stderr, entry);
+			fputs("\n"
+			      "InnoDB: record ", stderr);
+			rec_print_new(stderr, rec, offsets);
+			fprintf(stderr, "\nspace " UINT32PF " offset " UINT32PF
+				" (%u records, index id %llu)\n"
+				"InnoDB: Submit a detailed bug report"
+				" to https://jira.mariadb.org/\n",
+				block->page.id().space(),
+				block->page.id().page_no(),
+				(unsigned) page_get_n_recs(page),
+				(ulonglong) btr_page_get_index_id(page));
+
+			ut_ad(0);
+			return;
+		}
+
+		lock_update_delete(block, rec);
+
+		if (!page_zip) {
+			max_ins_size
+				= page_get_max_insert_size_after_reorganize(
+					page, 1);
+		}
+#ifdef UNIV_ZIP_DEBUG
+		ut_a(!page_zip || page_zip_validate(page_zip, page, index));
+#endif /* UNIV_ZIP_DEBUG */
+		page_cur_delete_rec(&page_cur, index, offsets, mtr);
+#ifdef UNIV_ZIP_DEBUG
+		ut_a(!page_zip || page_zip_validate(page_zip, page, index));
+#endif /* UNIV_ZIP_DEBUG */
+
+		if (page_zip) {
+			ibuf_update_free_bits_zip(block, mtr);
+		} else {
+			ibuf_update_free_bits_low(block, max_ins_size, mtr);
+		}
+
+		if (UNIV_LIKELY_NULL(heap)) {
+			mem_heap_free(heap);
+		}
+	} else {
+		/* The record must have been purged already. */
+	}
+}
+
+/*********************************************************************//**
+Restores insert buffer tree cursor position
+@return whether the position was restored */
+static MY_ATTRIBUTE((nonnull))
+bool
+ibuf_restore_pos(
+/*=============*/
+	const page_id_t	page_id,/*!< in: page identifier */
+	const dtuple_t*	search_tuple,
+				/*!< in: search tuple for entries of page_no */
+	ulint		mode,	/*!< in: BTR_MODIFY_LEAF or BTR_MODIFY_TREE */
+	btr_pcur_t*	pcur,	/*!< in/out: persistent cursor whose
+				position is to be restored */
+	mtr_t*		mtr)	/*!< in/out: mini-transaction */
+{
+	ut_ad(mode == BTR_MODIFY_LEAF
+	      || BTR_LATCH_MODE_WITHOUT_INTENTION(mode) == BTR_MODIFY_TREE);
+
+	if (UNIV_LIKELY(btr_pcur_restore_position(mode, pcur, mtr))) {
+		return true;
+	}
+
+	if (fil_space_t* s = fil_space_t::get(page_id.space())) {
+		ib::error() << "ibuf cursor restoration fails!"
+			" ibuf record inserted to page "
+			<< page_id
+			<< " in file " << s->chain.start->name;
+		s->release();
+
+		ib::error() << BUG_REPORT_MSG;
+
+		rec_print_old(stderr, btr_pcur_get_rec(pcur));
+		rec_print_old(stderr, pcur->old_rec);
+		dtuple_print(stderr, search_tuple);
+
+		rec_print_old(stderr,
+			      page_rec_get_next(btr_pcur_get_rec(pcur)));
+	}
+
+	ibuf_btr_pcur_commit_specify_mtr(pcur, mtr);
+	return false;
+}
+
+/**
+Delete a change buffer record.
+@param[in]	page_id		page identifier
+@param[in,out]	pcur		persistent cursor positioned on the record
+@param[in]	search_tuple	search key for (space,page_no)
+@param[in,out]	mtr		mini-transaction
+@return whether mtr was committed (due to pessimistic operation) */
+static MY_ATTRIBUTE((warn_unused_result, nonnull))
+bool ibuf_delete_rec(const page_id_t page_id, btr_pcur_t* pcur,
+		     const dtuple_t* search_tuple, mtr_t* mtr)
+{
+	ibool		success;
+	page_t*		root;
+	dberr_t		err;
+
+	ut_ad(ibuf_inside(mtr));
+	ut_ad(page_rec_is_user_rec(btr_pcur_get_rec(pcur)));
+	ut_ad(ibuf_rec_get_page_no(mtr, btr_pcur_get_rec(pcur))
+	      == page_id.page_no());
+	ut_ad(ibuf_rec_get_space(mtr, btr_pcur_get_rec(pcur))
+	      == page_id.space());
+
+	success = btr_cur_optimistic_delete(btr_pcur_get_btr_cur(pcur),
+					    0, mtr);
+
+	if (success) {
+		if (page_is_empty(btr_pcur_get_page(pcur))) {
+			/* If a B-tree page is empty, it must be the root page
+			and the whole B-tree must be empty. InnoDB does not
+			allow empty B-tree pages other than the root. */
+			root = btr_pcur_get_page(pcur);
+
+			ut_ad(page_get_space_id(root) == IBUF_SPACE_ID);
+			ut_ad(page_get_page_no(root)
+			      == FSP_IBUF_TREE_ROOT_PAGE_NO);
+
+			/* ibuf.empty is protected by the root page latch.
+			Before the deletion, it had to be FALSE. */
+			ut_ad(!ibuf.empty);
+			ibuf.empty = true;
+		}
+
+		return(FALSE);
+	}
+
+	/* We have to resort to a pessimistic delete from ibuf.
+	Delete-mark the record so that it will not be applied again,
+	in case the server crashes before the pessimistic delete is
+	made persistent. */
+	btr_rec_set_deleted<true>(btr_pcur_get_block(pcur),
+				  btr_pcur_get_rec(pcur), mtr);
+
+	btr_pcur_store_position(pcur, mtr);
+	ibuf_btr_pcur_commit_specify_mtr(pcur, mtr);
+
+	ibuf_mtr_start(mtr);
+	mutex_enter(&ibuf_mutex);
+
+	if (!ibuf_restore_pos(page_id, search_tuple,
+			      BTR_MODIFY_TREE | BTR_LATCH_FOR_DELETE,
+			      pcur, mtr)) {
+
+		mutex_exit(&ibuf_mutex);
+		ut_ad(mtr->has_committed());
+		goto func_exit;
+	}
+
+	root = ibuf_tree_root_get(mtr)->frame;
+
+	btr_cur_pessimistic_delete(&err, TRUE, btr_pcur_get_btr_cur(pcur), 0,
+				   false, mtr);
+	ut_a(err == DB_SUCCESS);
+
+	ibuf_size_update(root);
+	mutex_exit(&ibuf_mutex);
+
+	ibuf.empty = page_is_empty(root);
+	ibuf_btr_pcur_commit_specify_mtr(pcur, mtr);
+
+func_exit:
+	ut_ad(mtr->has_committed());
+	btr_pcur_close(pcur);
+
+	return(TRUE);
+}
+
+/** Check whether buffered changes exist for a page.
+@param[in]	id		page identifier
+@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
+@return whether buffered changes exist */
+bool ibuf_page_exists(const page_id_t id, ulint zip_size)
+{
+	ut_ad(!fsp_is_system_temporary(id.space()));
+
+	const ulint physical_size = zip_size ? zip_size : srv_page_size;
+
+	if (ibuf_fixed_addr_page(id, physical_size)
+	    || fsp_descr_page(id, physical_size)) {
+		return false;
+	}
+
+	mtr_t mtr;
+	bool bitmap_bits = false;
+
+	ibuf_mtr_start(&mtr);
+	if (const buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(
+		    id, zip_size, &mtr)) {
+		bitmap_bits = ibuf_bitmap_page_get_bits(
+			bitmap_page->frame, id, zip_size,
+			IBUF_BITMAP_BUFFERED, &mtr) != 0;
+	}
+	ibuf_mtr_commit(&mtr);
+	return bitmap_bits;
+}
+
+/** Reset the bits in the bitmap page for the given block and page id.
+@param b        X-latched secondary index page (nullptr to discard changes)
+@param page_id  page identifier
+@param zip_size ROW_FORMAT=COMPRESSED page size, or 0
+@param mtr      mini-transaction */
+static void ibuf_reset_bitmap(buf_block_t *b, page_id_t page_id,
+                              ulint zip_size, mtr_t *mtr)
+{
+ buf_block_t *bitmap= ibuf_bitmap_get_map_page(page_id, zip_size, mtr);
+ if (!bitmap)
+   return;
+
+ const ulint physical_size = zip_size ? zip_size : srv_page_size;
+ /* FIXME: update the bitmap byte only once! */
+ ibuf_bitmap_page_set_bits<IBUF_BITMAP_BUFFERED>(bitmap, page_id,
+                                                 physical_size, false, mtr);
+
+ if (b)
+   ibuf_bitmap_page_set_bits<IBUF_BITMAP_FREE>(bitmap, page_id, physical_size,
+                                               ibuf_index_page_calc_free(b),
+                                               mtr);
+}
+
+/** When an index page is read from a disk to the buffer pool, this function
+applies any buffered operations to the page and deletes the entries from the
+insert buffer. If the page is not read, but created in the buffer pool, this
+function deletes its buffered entries from the insert buffer; there can
+exist entries for such a page if the page belonged to an index which
+subsequently was dropped.
+@param block    X-latched page to try to apply changes to, or NULL to discard
+@param page_id  page identifier
+@param zip_size ROW_FORMAT=COMPRESSED page size, or 0 */
+void ibuf_merge_or_delete_for_page(buf_block_t *block, const page_id_t page_id,
+                                   ulint zip_size)
+{
+	if (trx_sys_hdr_page(page_id)) {
+		return;
+	}
+
+	btr_pcur_t	pcur;
+#ifdef UNIV_IBUF_DEBUG
+	ulint		volume			= 0;
+#endif /* UNIV_IBUF_DEBUG */
+	bool		corruption_noticed	= false;
+	mtr_t		mtr;
+
+	/* Counts for merged & discarded operations. */
+	ulint		mops[IBUF_OP_COUNT];
+	ulint		dops[IBUF_OP_COUNT];
+
+	ut_ad(!block || page_id == block->page.id());
+	ut_ad(!block || block->page.state() == BUF_BLOCK_FILE_PAGE);
+	ut_ad(!block || block->page.status == buf_page_t::NORMAL);
+	ut_ad(!trx_sys_hdr_page(page_id));
+	ut_ad(page_id < page_id_t(SRV_SPACE_ID_UPPER_BOUND, 0));
+
+	const ulint physical_size = zip_size ? zip_size : srv_page_size;
+
+	if (ibuf_fixed_addr_page(page_id, physical_size)
+	    || fsp_descr_page(page_id, physical_size)) {
+		return;
+	}
+
+	fil_space_t* space = fil_space_t::get(page_id.space());
+
+	if (UNIV_UNLIKELY(!space)) {
+		block = NULL;
+	} else {
+		ulint	bitmap_bits = 0;
+
+		ibuf_mtr_start(&mtr);
+
+		buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(
+			page_id, zip_size, &mtr);
+
+		if (bitmap_page
+		    && fil_page_get_type(bitmap_page->frame)
+		    != FIL_PAGE_TYPE_ALLOCATED) {
+			bitmap_bits = ibuf_bitmap_page_get_bits(
+				bitmap_page->frame, page_id, zip_size,
+				IBUF_BITMAP_BUFFERED, &mtr);
+		}
+
+		ibuf_mtr_commit(&mtr);
+
+		if (bitmap_bits && fseg_page_is_free(
+				space, page_id.page_no())) {
+			ibuf_mtr_start(&mtr);
+			mtr.set_named_space(space);
+			ibuf_reset_bitmap(block, page_id, zip_size, &mtr);
+			ibuf_mtr_commit(&mtr);
+			bitmap_bits = 0;
+		}
+
+		if (!bitmap_bits) {
+			/* No changes are buffered for this page. */
+			space->release();
+			return;
+		}
+	}
+
+	mem_heap_t* heap = mem_heap_create(512);
+
+	const dtuple_t* search_tuple = ibuf_search_tuple_build(
+		page_id.space(), page_id.page_no(), heap);
+
+	if (block != NULL) {
+		/* Move the ownership of the x-latch on the page to this OS
+		thread, so that we can acquire a second x-latch on it. This
+		is needed for the insert operations to the index page to pass
+		the debug checks. */
+
+		rw_lock_x_lock_move_ownership(&(block->lock));
+
+		if (!fil_page_index_page_check(block->frame)
+		    || !page_is_leaf(block->frame)) {
+
+			corruption_noticed = true;
+
+			ib::error() << "Corruption in the tablespace. Bitmap"
+				" shows insert buffer records to page "
+				<< page_id << " though the page type is "
+				<< fil_page_get_type(block->frame)
+				<< ", which is not an index leaf page. We try"
+				" to resolve the problem by skipping the"
+				" insert buffer merge for this page. Please"
+				" run CHECK TABLE on your tables to determine"
+				" if they are corrupt after this.";
+			ut_ad(0);
+		}
+	}
+
+	memset(mops, 0, sizeof(mops));
+	memset(dops, 0, sizeof(dops));
+
+loop:
+	ibuf_mtr_start(&mtr);
+
+	/* Position pcur in the insert buffer at the first entry for this
+	index page */
+	btr_pcur_open_on_user_rec(
+		ibuf.index, search_tuple, PAGE_CUR_GE, BTR_MODIFY_LEAF,
+		&pcur, &mtr);
+
+	if (block) {
+		ut_ad(rw_lock_own(&block->lock, RW_LOCK_X));
+		buf_block_buf_fix_inc(block, __FILE__, __LINE__);
+		rw_lock_x_lock(&block->lock);
+
+		mtr.memo_push(block, MTR_MEMO_PAGE_X_FIX);
+		/* This is a user page (secondary index leaf page),
+		but we pretend that it is a change buffer page in
+		order to obey the latching order. This should be OK,
+		because buffered changes are applied immediately while
+		the block is io-fixed. Other threads must not try to
+		latch an io-fixed block. */
+		buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE);
+	}
+
+	if (space) {
+		mtr.set_named_space(space);
+	}
+
+	if (!btr_pcur_is_on_user_rec(&pcur)) {
+		ut_ad(btr_pcur_is_after_last_on_page(&pcur));
+		goto reset_bit;
+	}
+
+	for (;;) {
+		rec_t*	rec;
+
+		ut_ad(btr_pcur_is_on_user_rec(&pcur));
+
+		rec = btr_pcur_get_rec(&pcur);
+
+		/* Check if the entry is for this index page */
+		if (ibuf_rec_get_page_no(&mtr, rec) != page_id.page_no()
+		    || ibuf_rec_get_space(&mtr, rec) != page_id.space()) {
+
+			if (block != NULL) {
+				page_header_reset_last_insert(block, &mtr);
+			}
+
+			goto reset_bit;
+		}
+
+		if (corruption_noticed) {
+			fputs("InnoDB: Discarding record\n ", stderr);
+			rec_print_old(stderr, rec);
+			fputs("\nInnoDB: from the insert buffer!\n\n", stderr);
+		} else if (block != NULL && !rec_get_deleted_flag(rec, 0)) {
+			/* Now we have at pcur a record which should be
+			applied on the index page; NOTE that the call below
+			copies pointers to fields in rec, and we must
+			keep the latch to the rec page until the
+			insertion is finished! */
+			dtuple_t*	entry;
+			trx_id_t	max_trx_id;
+			dict_index_t*	dummy_index;
+			ibuf_op_t	op = ibuf_rec_get_op_type(&mtr, rec);
+
+			max_trx_id = page_get_max_trx_id(page_align(rec));
+			page_update_max_trx_id(block,
+					       buf_block_get_page_zip(block),
+					       max_trx_id, &mtr);
+
+			ut_ad(page_validate(page_align(rec), ibuf.index));
+
+			entry = ibuf_build_entry_from_ibuf_rec(
+				&mtr, rec, heap, &dummy_index);
+			ut_ad(!dummy_index->table->space);
+			dummy_index->table->space = space;
+			dummy_index->table->space_id = space->id;
+
+			ut_ad(page_validate(block->frame, dummy_index));
+
+			switch (op) {
+			case IBUF_OP_INSERT:
+#ifdef UNIV_IBUF_DEBUG
+				volume += rec_get_converted_size(
+					dummy_index, entry, 0);
+
+				volume += page_dir_calc_reserved_space(1);
+
+				ut_a(volume <= (4U << srv_page_size_shift)
+				     / IBUF_PAGE_SIZE_PER_FREE_SPACE);
+#endif
+				ibuf_insert_to_index_page(
+					entry, block, dummy_index, &mtr);
+				break;
+
+			case IBUF_OP_DELETE_MARK:
+				ibuf_set_del_mark(
+					entry, block, dummy_index, &mtr);
+				break;
+
+			case IBUF_OP_DELETE:
+				ibuf_delete(entry, block, dummy_index, &mtr);
+				/* Because ibuf_delete() will latch an
+				insert buffer bitmap page, commit mtr
+				before latching any further pages.
+				Store and restore the cursor position. */
+				ut_ad(rec == btr_pcur_get_rec(&pcur));
+				ut_ad(page_rec_is_user_rec(rec));
+				ut_ad(ibuf_rec_get_page_no(&mtr, rec)
+				      == page_id.page_no());
+				ut_ad(ibuf_rec_get_space(&mtr, rec)
+				      == page_id.space());
+
+				/* Mark the change buffer record processed,
+				so that it will not be merged again in case
+				the server crashes between the following
+				mtr_commit() and the subsequent mtr_commit()
+				of deleting the change buffer record. */
+				btr_rec_set_deleted<true>(
+					btr_pcur_get_block(&pcur),
+					btr_pcur_get_rec(&pcur), &mtr);
+
+				btr_pcur_store_position(&pcur, &mtr);
+				ibuf_btr_pcur_commit_specify_mtr(&pcur, &mtr);
+
+				ibuf_mtr_start(&mtr);
+				mtr.set_named_space(space);
+
+				ut_ad(rw_lock_own(&block->lock, RW_LOCK_X));
+				buf_block_buf_fix_inc(block,
+						      __FILE__, __LINE__);
+				rw_lock_x_lock(&block->lock);
+				mtr.memo_push(block, MTR_MEMO_PAGE_X_FIX);
+
+				/* This is a user page (secondary
+				index leaf page), but it should be OK
+				to use too low latching order for it,
+				as the block is io-fixed. */
+				buf_block_dbg_add_level(
+					block, SYNC_IBUF_TREE_NODE);
+
+				if (!ibuf_restore_pos(page_id, search_tuple,
+						      BTR_MODIFY_LEAF,
+						      &pcur, &mtr)) {
+
+					ut_ad(mtr.has_committed());
+					mops[op]++;
+					ibuf_dummy_index_free(dummy_index);
+					goto loop;
+				}
+
+				break;
+			default:
+				ut_error;
+			}
+
+			mops[op]++;
+
+			ibuf_dummy_index_free(dummy_index);
+		} else {
+			dops[ibuf_rec_get_op_type(&mtr, rec)]++;
+		}
+
+		/* Delete the record from ibuf */
+		if (ibuf_delete_rec(page_id, &pcur, search_tuple, &mtr)) {
+			/* Deletion was pessimistic and mtr was committed:
+			we start from the beginning again */
+
+			ut_ad(mtr.has_committed());
+			goto loop;
+		} else if (btr_pcur_is_after_last_on_page(&pcur)) {
+			ibuf_mtr_commit(&mtr);
+			btr_pcur_close(&pcur);
+
+			goto loop;
+		}
+	}
+
+reset_bit:
+	if (space) {
+		ibuf_reset_bitmap(block, page_id, zip_size, &mtr);
+	}
+
+	ibuf_mtr_commit(&mtr);
+
+	if (space) {
+		space->release();
+	}
+
+	btr_pcur_close(&pcur);
+	mem_heap_free(heap);
+
+	ibuf.n_merges++;
+	ibuf_add_ops(ibuf.n_merged_ops, mops);
+	ibuf_add_ops(ibuf.n_discarded_ops, dops);
+}
+
+/** Delete all change buffer entries for a tablespace,
+in DISCARD TABLESPACE, IMPORT TABLESPACE, or crash recovery.
+@param[in]	space		missing or to-be-discarded tablespace */
+void ibuf_delete_for_discarded_space(ulint space)
+{
+	mem_heap_t*	heap;
+	btr_pcur_t	pcur;
+	dtuple_t*	search_tuple;
+	const rec_t*	ibuf_rec;
+	mtr_t		mtr;
+
+	/* Counts for discarded operations. */
+	ulint		dops[IBUF_OP_COUNT];
+
+	heap = mem_heap_create(512);
+
+	/* Use page number 0 to build the search tuple so that we get the
+	cursor positioned at the first entry for this space id */
+
+	search_tuple = ibuf_search_tuple_build(space, 0, heap);
+
+	memset(dops, 0, sizeof(dops));
+loop:
+	ibuf_mtr_start(&mtr);
+
+	/* Position pcur in the insert buffer at the first entry for the
+	space */
+	btr_pcur_open_on_user_rec(
+		ibuf.index, search_tuple, PAGE_CUR_GE, BTR_MODIFY_LEAF,
+		&pcur, &mtr);
+
+	if (!btr_pcur_is_on_user_rec(&pcur)) {
+		ut_ad(btr_pcur_is_after_last_on_page(&pcur));
+		goto leave_loop;
+	}
+
+	for (;;) {
+		ut_ad(btr_pcur_is_on_user_rec(&pcur));
+
+		ibuf_rec = btr_pcur_get_rec(&pcur);
+
+		/* Check if the entry is for this space */
+		if (ibuf_rec_get_space(&mtr, ibuf_rec) != space) {
+
+			goto leave_loop;
+		}
+
+		uint32_t page_no = ibuf_rec_get_page_no(&mtr, ibuf_rec);
+
+		dops[ibuf_rec_get_op_type(&mtr, ibuf_rec)]++;
+
+		/* Delete the record from ibuf */
+		if (ibuf_delete_rec(page_id_t(space, page_no),
+				    &pcur, search_tuple, &mtr)) {
+			/* Deletion was pessimistic and mtr was committed:
+			we start from the beginning again */
+
+			ut_ad(mtr.has_committed());
+			goto loop;
+		}
+
+		if (btr_pcur_is_after_last_on_page(&pcur)) {
+			ibuf_mtr_commit(&mtr);
+			btr_pcur_close(&pcur);
+
+			goto loop;
+		}
+	}
+
+leave_loop:
+	ibuf_mtr_commit(&mtr);
+	btr_pcur_close(&pcur);
+
+	ibuf_add_ops(ibuf.n_discarded_ops, dops);
+
+	mem_heap_free(heap);
+}
+
+/******************************************************************//**
+Looks if the insert buffer is empty.
+@return true if empty */
+bool
+ibuf_is_empty(void)
+/*===============*/
+{
+	mtr_t		mtr;
+
+	ibuf_mtr_start(&mtr);
+
+	ut_d(mutex_enter(&ibuf_mutex));
+	const buf_block_t* root = ibuf_tree_root_get(&mtr);
+	bool is_empty = page_is_empty(root->frame);
+	ut_a(is_empty == ibuf.empty);
+	ut_d(mutex_exit(&ibuf_mutex));
+	ibuf_mtr_commit(&mtr);
+
+	return(is_empty);
+}
+
+/******************************************************************//**
+Prints info of ibuf. */
+void
+ibuf_print(
+/*=======*/
+	FILE*	file)	/*!< in: file where to print */
+{
+	mutex_enter(&ibuf_mutex);
+
+	fprintf(file,
+		"Ibuf: size " ULINTPF ", free list len " ULINTPF ","
+		" seg size " ULINTPF ", " ULINTPF " merges\n",
+		ibuf.size,
+		ibuf.free_list_len,
+		ibuf.seg_size,
+		ulint{ibuf.n_merges});
+
+	fputs("merged operations:\n ", file);
+	ibuf_print_ops(ibuf.n_merged_ops, file);
+
+	fputs("discarded operations:\n ", file);
+	ibuf_print_ops(ibuf.n_discarded_ops, file);
+
+	mutex_exit(&ibuf_mutex);
+}
+
+/** Check the insert buffer bitmaps on IMPORT TABLESPACE.
+@param[in]	trx	transaction
+@param[in,out]	space	tablespace being imported
+@return DB_SUCCESS or error code */
+dberr_t ibuf_check_bitmap_on_import(const trx_t* trx, fil_space_t* space)
+{
+	ut_ad(trx->mysql_thd);
+	ut_ad(space->purpose == FIL_TYPE_IMPORT);
+
+	const unsigned zip_size = space->zip_size();
+	const unsigned physical_size = space->physical_size();
+
+	uint32_t size= std::min(space->free_limit, space->size);
+
+	if (size == 0) {
+		return(DB_TABLE_NOT_FOUND);
+	}
+
+	mtr_t mtr;
+
+	mutex_enter(&ibuf_mutex);
+
+	/* The two bitmap pages (allocation bitmap and ibuf bitmap) repeat
+	every page_size pages. For example if page_size is 16 KiB, then the
+	two bitmap pages repeat every 16 KiB * 16384 = 256 MiB. In the loop
+	below page_no is measured in number of pages since the beginning of
+	the space, as usual. */
+
+	for (uint32_t page_no = 0; page_no < size; page_no += physical_size) {
+		if (trx_is_interrupted(trx)) {
+			mutex_exit(&ibuf_mutex);
+			return(DB_INTERRUPTED);
+		}
+
+		mtr_start(&mtr);
+
+		mtr_set_log_mode(&mtr, MTR_LOG_NO_REDO);
+
+		ibuf_enter(&mtr);
+
+		buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(
+			page_id_t(space->id, page_no), zip_size, &mtr);
+		if (!bitmap_page) {
+			mutex_exit(&ibuf_mutex);
+			mtr.commit();
+			return DB_CORRUPTION;
+		}
+
+		if (buf_is_zeroes(span<const byte>(bitmap_page->frame,
+						   physical_size))) {
+			/* This means we got all-zero page instead of
+			ibuf bitmap page. The subsequent page should be
+			all-zero pages. */
+#ifdef UNIV_DEBUG
+			for (uint32_t curr_page = page_no + 1;
+			     curr_page < physical_size; curr_page++) {
+
+				buf_block_t* block = buf_page_get(
+					page_id_t(space->id, curr_page),
+					zip_size, RW_S_LATCH, &mtr);
+	                        page_t*	page = buf_block_get_frame(block);
+				ut_ad(buf_is_zeroes(span<const byte>(
+							    page,
+							    physical_size)));
+			}
+#endif /* UNIV_DEBUG */
+			ibuf_exit(&mtr);
+			mtr_commit(&mtr);
+			continue;
+		}
+
+		for (uint32_t i = FSP_IBUF_BITMAP_OFFSET + 1; i < physical_size;
+		     i++) {
+			const uint32_t offset = page_no + i;
+			const page_id_t	cur_page_id(space->id, offset);
+
+			if (ibuf_bitmap_page_get_bits(
+				    bitmap_page->frame, cur_page_id, zip_size,
+				    IBUF_BITMAP_IBUF, &mtr)) {
+
+				mutex_exit(&ibuf_mutex);
+				ibuf_exit(&mtr);
+				mtr_commit(&mtr);
+
+				ib_errf(trx->mysql_thd,
+					IB_LOG_LEVEL_ERROR,
+					 ER_INNODB_INDEX_CORRUPT,
+					 "File %s page %u"
+					 " is wrongly flagged to belong to the"
+					 " insert buffer",
+					space->chain.start->name, offset);
+				return(DB_CORRUPTION);
+			}
+
+			if (ibuf_bitmap_page_get_bits(
+				    bitmap_page->frame, cur_page_id, zip_size,
+				    IBUF_BITMAP_BUFFERED, &mtr)) {
+
+				ib_errf(trx->mysql_thd,
+					IB_LOG_LEVEL_WARN,
+					ER_INNODB_INDEX_CORRUPT,
+					"Buffered changes"
+					" for file %s page %u are lost",
+					space->chain.start->name, offset);
+
+				/* Tolerate this error, so that
+				slightly corrupted tables can be
+				imported and dumped.  Clear the bit. */
+				ibuf_bitmap_page_set_bits<IBUF_BITMAP_BUFFERED>(
+					bitmap_page, cur_page_id,
+					physical_size, false, &mtr);
+			}
+		}
+
+		ibuf_exit(&mtr);
+		mtr_commit(&mtr);
+	}
+
+	mutex_exit(&ibuf_mutex);
+	return(DB_SUCCESS);
+}
+
+/** Updates free bits and buffered bits for bulk loaded page.
+@param[in]	block	index page
+@param[in]	reset	flag if reset free val */
+void
+ibuf_set_bitmap_for_bulk_load(
+	buf_block_t*	block,
+	bool		reset)
+{
+	mtr_t	mtr;
+	ulint	free_val;
+
+	ut_a(page_is_leaf(buf_block_get_frame(block)));
+
+	free_val = ibuf_index_page_calc_free(block);
+
+	mtr.start();
+	fil_space_t* space = mtr.set_named_space_id(block->page.id().space());
+
+	buf_block_t* bitmap_page = ibuf_bitmap_get_map_page(block->page.id(),
+							    space->zip_size(),
+							    &mtr);
+
+	free_val = reset ? 0 : ibuf_index_page_calc_free(block);
+	/* FIXME: update the bitmap byte only once! */
+	ibuf_bitmap_page_set_bits<IBUF_BITMAP_FREE>(
+		bitmap_page, block->page.id(), block->physical_size(),
+		free_val, &mtr);
+
+	ibuf_bitmap_page_set_bits<IBUF_BITMAP_BUFFERED>(
+		bitmap_page, block->page.id(), block->physical_size(),
+		false, &mtr);
+
+	mtr.commit();
+}