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+/*****************************************************************************
+
+Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2017, 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 include/buf0lru.h
+The database buffer pool LRU replacement algorithm
+
+Created 11/5/1995 Heikki Tuuri
+*******************************************************/
+
+#pragma once
+
+#include "buf0types.h"
+#include "hash0hash.h"
+
+// Forward declaration
+struct trx_t;
+struct fil_space_t;
+
+/** Flush this many pages in buf_LRU_get_free_block() */
+extern size_t innodb_lru_flush_size;
+
+/*#######################################################################
+These are low-level functions
+#########################################################################*/
+
+/** Minimum LRU list length for which the LRU_old pointer is defined */
+#define BUF_LRU_OLD_MIN_LEN	512	/* 8 megabytes of 16k pages */
+
+/** Try to free a block. If bpage is a descriptor of a compressed-only
+ROW_FORMAT=COMPRESSED page, the buf_page_t object will be freed as well.
+The caller must hold buf_pool.mutex.
+@param bpage      block to be freed
+@param zip        whether to remove both copies of a ROW_FORMAT=COMPRESSED page
+@retval true if freed and buf_pool.mutex may have been temporarily released
+@retval false if the page was not freed */
+bool buf_LRU_free_page(buf_page_t *bpage, bool zip)
+  MY_ATTRIBUTE((nonnull));
+
+/** Try to free a replaceable block.
+@param limit  maximum number of blocks to scan
+@return true if found and freed */
+bool buf_LRU_scan_and_free_block(ulint limit= ULINT_UNDEFINED);
+
+/** @return a buffer block from the buf_pool.free list
+@retval	NULL	if the free list is empty */
+buf_block_t* buf_LRU_get_free_only();
+
+/** Get a block from the buf_pool.free list.
+If the list is empty, blocks will be moved from the end of buf_pool.LRU
+to buf_pool.free.
+
+This function is called from a user thread when it needs a clean
+block to read in a page. Note that we only ever get a block from
+the free list. Even when we flush a page or find a page in LRU scan
+we put it to free list to be used.
+* iteration 0:
+  * get a block from the buf_pool.free list, success:done
+  * if buf_pool.try_LRU_scan is set
+    * scan LRU up to 100 pages to free a clean block
+    * success:retry the free list
+  * flush up to innodb_lru_flush_size LRU blocks to data files
+    (until UT_LIST_GET_GEN(buf_pool.free) < innodb_lru_scan_depth)
+    * on buf_page_write_complete() the blocks will put on buf_pool.free list
+    * success: retry the free list
+* subsequent iterations: same as iteration 0 except:
+  * scan whole LRU list
+  * scan LRU list even if buf_pool.try_LRU_scan is not set
+
+@param have_mutex  whether buf_pool.mutex is already being held
+@return the free control block, in state BUF_BLOCK_MEMORY */
+buf_block_t* buf_LRU_get_free_block(bool have_mutex)
+	MY_ATTRIBUTE((malloc,warn_unused_result));
+
+/** @return whether the unzip_LRU list should be used for evicting a victim
+instead of the general LRU list */
+bool buf_LRU_evict_from_unzip_LRU();
+
+/** Puts a block back to the free list.
+@param[in]	block	block; not containing a file page */
+void
+buf_LRU_block_free_non_file_page(buf_block_t* block);
+/******************************************************************//**
+Adds a block to the LRU list. Please make sure that the page_size is
+already set when invoking the function, so that we can get correct
+page_size from the buffer page when adding a block into LRU */
+void
+buf_LRU_add_block(
+/*==============*/
+	buf_page_t*	bpage,	/*!< in: control block */
+	bool		old);	/*!< in: true if should be put to the old
+				blocks in the LRU list, else put to the
+				start; if the LRU list is very short, added to
+				the start regardless of this parameter */
+/******************************************************************//**
+Adds a block to the LRU list of decompressed zip pages. */
+void
+buf_unzip_LRU_add_block(
+/*====================*/
+	buf_block_t*	block,	/*!< in: control block */
+	ibool		old);	/*!< in: TRUE if should be put to the end
+				of the list, else put to the start */
+
+/** Update buf_pool.LRU_old_ratio.
+@param[in]	old_pct		Reserve this percentage of
+				the buffer pool for "old" blocks
+@param[in]	adjust		true=adjust the LRU list;
+				false=just assign buf_pool.LRU_old_ratio
+				during the initialization of InnoDB
+@return updated old_pct */
+uint buf_LRU_old_ratio_update(uint old_pct, bool adjust);
+/********************************************************************//**
+Update the historical stats that we are collecting for LRU eviction
+policy at the end of each interval. */
+void
+buf_LRU_stat_update();
+
+#ifdef UNIV_DEBUG
+/** Validate the LRU list. */
+void buf_LRU_validate();
+#endif /* UNIV_DEBUG */
+#if defined UNIV_DEBUG_PRINT || defined UNIV_DEBUG
+/** Dump the LRU list to stderr. */
+void buf_LRU_print();
+#endif /* UNIV_DEBUG_PRINT || UNIV_DEBUG */
+
+/** @name Heuristics for detecting index scan @{ */
+/** The denominator of buf_pool.LRU_old_ratio. */
+#define BUF_LRU_OLD_RATIO_DIV	1024
+/** Maximum value of buf_pool.LRU_old_ratio.
+@see buf_LRU_old_adjust_len
+@see buf_pool.LRU_old_ratio_update */
+#define BUF_LRU_OLD_RATIO_MAX	BUF_LRU_OLD_RATIO_DIV
+/** Minimum value of buf_pool.LRU_old_ratio.
+@see buf_LRU_old_adjust_len
+@see buf_pool.LRU_old_ratio_update
+The minimum must exceed
+(BUF_LRU_OLD_TOLERANCE + 5) * BUF_LRU_OLD_RATIO_DIV / BUF_LRU_OLD_MIN_LEN. */
+#define BUF_LRU_OLD_RATIO_MIN	51
+
+#if BUF_LRU_OLD_RATIO_MIN >= BUF_LRU_OLD_RATIO_MAX
+# error "BUF_LRU_OLD_RATIO_MIN >= BUF_LRU_OLD_RATIO_MAX"
+#endif
+#if BUF_LRU_OLD_RATIO_MAX > BUF_LRU_OLD_RATIO_DIV
+# error "BUF_LRU_OLD_RATIO_MAX > BUF_LRU_OLD_RATIO_DIV"
+#endif
+
+/** Move blocks to "new" LRU list only if the first access was at
+least this many milliseconds ago.  Not protected by any mutex or latch. */
+extern uint	buf_LRU_old_threshold_ms;
+/* @} */
+
+/** @brief Statistics for selecting the LRU list for eviction.
+
+These statistics are not 'of' LRU but 'for' LRU.  We keep count of I/O
+and page_zip_decompress() operations.  Based on the statistics we decide
+if we want to evict from buf_pool.unzip_LRU or buf_pool.LRU. */
+struct buf_LRU_stat_t
+{
+	ulint	io;	/**< Counter of buffer pool I/O operations. */
+	ulint	unzip;	/**< Counter of page_zip_decompress operations. */
+};
+
+/** Current operation counters.  Not protected by any mutex.
+Cleared by buf_LRU_stat_update(). */
+extern buf_LRU_stat_t	buf_LRU_stat_cur;
+
+/** Running sum of past values of buf_LRU_stat_cur.
+Updated by buf_LRU_stat_update().  Protected by buf_pool.mutex. */
+extern buf_LRU_stat_t	buf_LRU_stat_sum;
+
+/********************************************************************//**
+Increments the I/O counter in buf_LRU_stat_cur. */
+#define buf_LRU_stat_inc_io() buf_LRU_stat_cur.io++
+/********************************************************************//**
+Increments the page_zip_decompress() counter in buf_LRU_stat_cur. */
+#define buf_LRU_stat_inc_unzip() buf_LRU_stat_cur.unzip++