Adding upstream version 14.5.upstream/14.5upstream

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

1 files changed, 920 insertions, 0 deletions

diff --git a/src/backend/access/brin/brin_pageops.c b/src/backend/access/brin/brin_pageops.c
new file mode 100644
index 0000000..992b33a
--- /dev/null
+++ b/src/backend/access/brin/brin_pageops.c
@@ -0,0 +1,920 @@
+/*
+ * brin_pageops.c
+ *		Page-handling routines for BRIN indexes
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/brin/brin_pageops.c
+ */
+#include "postgres.h"
+
+#include "access/brin_page.h"
+#include "access/brin_pageops.h"
+#include "access/brin_revmap.h"
+#include "access/brin_xlog.h"
+#include "access/xloginsert.h"
+#include "miscadmin.h"
+#include "storage/bufmgr.h"
+#include "storage/freespace.h"
+#include "storage/lmgr.h"
+#include "storage/smgr.h"
+#include "utils/rel.h"
+
+/*
+ * Maximum size of an entry in a BRIN_PAGETYPE_REGULAR page.  We can tolerate
+ * a single item per page, unlike other index AMs.
+ */
+#define BrinMaxItemSize \
+	MAXALIGN_DOWN(BLCKSZ - \
+				  (MAXALIGN(SizeOfPageHeaderData + \
+							sizeof(ItemIdData)) + \
+				   MAXALIGN(sizeof(BrinSpecialSpace))))
+
+static Buffer brin_getinsertbuffer(Relation irel, Buffer oldbuf, Size itemsz,
+								   bool *extended);
+static Size br_page_get_freespace(Page page);
+static void brin_initialize_empty_new_buffer(Relation idxrel, Buffer buffer);
+
+
+/*
+ * Update tuple origtup (size origsz), located in offset oldoff of buffer
+ * oldbuf, to newtup (size newsz) as summary tuple for the page range starting
+ * at heapBlk.  oldbuf must not be locked on entry, and is not locked at exit.
+ *
+ * If samepage is true, attempt to put the new tuple in the same page, but if
+ * there's no room, use some other one.
+ *
+ * If the update is successful, return true; the revmap is updated to point to
+ * the new tuple.  If the update is not done for whatever reason, return false.
+ * Caller may retry the update if this happens.
+ */
+bool
+brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
+			  BrinRevmap *revmap, BlockNumber heapBlk,
+			  Buffer oldbuf, OffsetNumber oldoff,
+			  const BrinTuple *origtup, Size origsz,
+			  const BrinTuple *newtup, Size newsz,
+			  bool samepage)
+{
+	Page		oldpage;
+	ItemId		oldlp;
+	BrinTuple  *oldtup;
+	Size		oldsz;
+	Buffer		newbuf;
+	BlockNumber newblk = InvalidBlockNumber;
+	bool		extended;
+
+	Assert(newsz == MAXALIGN(newsz));
+
+	/* If the item is oversized, don't bother. */
+	if (newsz > BrinMaxItemSize)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("index row size %zu exceeds maximum %zu for index \"%s\"",
+						newsz, BrinMaxItemSize, RelationGetRelationName(idxrel))));
+		return false;			/* keep compiler quiet */
+	}
+
+	/* make sure the revmap is long enough to contain the entry we need */
+	brinRevmapExtend(revmap, heapBlk);
+
+	if (!samepage)
+	{
+		/* need a page on which to put the item */
+		newbuf = brin_getinsertbuffer(idxrel, oldbuf, newsz, &extended);
+		if (!BufferIsValid(newbuf))
+		{
+			Assert(!extended);
+			return false;
+		}
+
+		/*
+		 * Note: it's possible (though unlikely) that the returned newbuf is
+		 * the same as oldbuf, if brin_getinsertbuffer determined that the old
+		 * buffer does in fact have enough space.
+		 */
+		if (newbuf == oldbuf)
+		{
+			Assert(!extended);
+			newbuf = InvalidBuffer;
+		}
+		else
+			newblk = BufferGetBlockNumber(newbuf);
+	}
+	else
+	{
+		LockBuffer(oldbuf, BUFFER_LOCK_EXCLUSIVE);
+		newbuf = InvalidBuffer;
+		extended = false;
+	}
+	oldpage = BufferGetPage(oldbuf);
+	oldlp = PageGetItemId(oldpage, oldoff);
+
+	/*
+	 * Check that the old tuple wasn't updated concurrently: it might have
+	 * moved someplace else entirely, and for that matter the whole page
+	 * might've become a revmap page.  Note that in the first two cases
+	 * checked here, the "oldlp" we just calculated is garbage; but
+	 * PageGetItemId() is simple enough that it was safe to do that
+	 * calculation anyway.
+	 */
+	if (!BRIN_IS_REGULAR_PAGE(oldpage) ||
+		oldoff > PageGetMaxOffsetNumber(oldpage) ||
+		!ItemIdIsNormal(oldlp))
+	{
+		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
+
+		/*
+		 * If this happens, and the new buffer was obtained by extending the
+		 * relation, then we need to ensure we don't leave it uninitialized or
+		 * forget about it.
+		 */
+		if (BufferIsValid(newbuf))
+		{
+			if (extended)
+				brin_initialize_empty_new_buffer(idxrel, newbuf);
+			UnlockReleaseBuffer(newbuf);
+			if (extended)
+				FreeSpaceMapVacuumRange(idxrel, newblk, newblk + 1);
+		}
+		return false;
+	}
+
+	oldsz = ItemIdGetLength(oldlp);
+	oldtup = (BrinTuple *) PageGetItem(oldpage, oldlp);
+
+	/*
+	 * ... or it might have been updated in place to different contents.
+	 */
+	if (!brin_tuples_equal(oldtup, oldsz, origtup, origsz))
+	{
+		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
+		if (BufferIsValid(newbuf))
+		{
+			/* As above, initialize and record new page if we got one */
+			if (extended)
+				brin_initialize_empty_new_buffer(idxrel, newbuf);
+			UnlockReleaseBuffer(newbuf);
+			if (extended)
+				FreeSpaceMapVacuumRange(idxrel, newblk, newblk + 1);
+		}
+		return false;
+	}
+
+	/*
+	 * Great, the old tuple is intact.  We can proceed with the update.
+	 *
+	 * If there's enough room in the old page for the new tuple, replace it.
+	 *
+	 * Note that there might now be enough space on the page even though the
+	 * caller told us there isn't, if a concurrent update moved another tuple
+	 * elsewhere or replaced a tuple with a smaller one.
+	 */
+	if (((BrinPageFlags(oldpage) & BRIN_EVACUATE_PAGE) == 0) &&
+		brin_can_do_samepage_update(oldbuf, origsz, newsz))
+	{
+		START_CRIT_SECTION();
+		if (!PageIndexTupleOverwrite(oldpage, oldoff, (Item) unconstify(BrinTuple *, newtup), newsz))
+			elog(ERROR, "failed to replace BRIN tuple");
+		MarkBufferDirty(oldbuf);
+
+		/* XLOG stuff */
+		if (RelationNeedsWAL(idxrel))
+		{
+			xl_brin_samepage_update xlrec;
+			XLogRecPtr	recptr;
+			uint8		info = XLOG_BRIN_SAMEPAGE_UPDATE;
+
+			xlrec.offnum = oldoff;
+
+			XLogBeginInsert();
+			XLogRegisterData((char *) &xlrec, SizeOfBrinSamepageUpdate);
+
+			XLogRegisterBuffer(0, oldbuf, REGBUF_STANDARD);
+			XLogRegisterBufData(0, (char *) unconstify(BrinTuple *, newtup), newsz);
+
+			recptr = XLogInsert(RM_BRIN_ID, info);
+
+			PageSetLSN(oldpage, recptr);
+		}
+
+		END_CRIT_SECTION();
+
+		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
+
+		if (BufferIsValid(newbuf))
+		{
+			/* As above, initialize and record new page if we got one */
+			if (extended)
+				brin_initialize_empty_new_buffer(idxrel, newbuf);
+			UnlockReleaseBuffer(newbuf);
+			if (extended)
+				FreeSpaceMapVacuumRange(idxrel, newblk, newblk + 1);
+		}
+
+		return true;
+	}
+	else if (newbuf == InvalidBuffer)
+	{
+		/*
+		 * Not enough space, but caller said that there was. Tell them to
+		 * start over.
+		 */
+		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
+		return false;
+	}
+	else
+	{
+		/*
+		 * Not enough free space on the oldpage. Put the new tuple on the new
+		 * page, and update the revmap.
+		 */
+		Page		newpage = BufferGetPage(newbuf);
+		Buffer		revmapbuf;
+		ItemPointerData newtid;
+		OffsetNumber newoff;
+		Size		freespace = 0;
+
+		revmapbuf = brinLockRevmapPageForUpdate(revmap, heapBlk);
+
+		START_CRIT_SECTION();
+
+		/*
+		 * We need to initialize the page if it's newly obtained.  Note we
+		 * will WAL-log the initialization as part of the update, so we don't
+		 * need to do that here.
+		 */
+		if (extended)
+			brin_page_init(newpage, BRIN_PAGETYPE_REGULAR);
+
+		PageIndexTupleDeleteNoCompact(oldpage, oldoff);
+		newoff = PageAddItem(newpage, (Item) unconstify(BrinTuple *, newtup), newsz,
+							 InvalidOffsetNumber, false, false);
+		if (newoff == InvalidOffsetNumber)
+			elog(ERROR, "failed to add BRIN tuple to new page");
+		MarkBufferDirty(oldbuf);
+		MarkBufferDirty(newbuf);
+
+		/* needed to update FSM below */
+		if (extended)
+			freespace = br_page_get_freespace(newpage);
+
+		ItemPointerSet(&newtid, newblk, newoff);
+		brinSetHeapBlockItemptr(revmapbuf, pagesPerRange, heapBlk, newtid);
+		MarkBufferDirty(revmapbuf);
+
+		/* XLOG stuff */
+		if (RelationNeedsWAL(idxrel))
+		{
+			xl_brin_update xlrec;
+			XLogRecPtr	recptr;
+			uint8		info;
+
+			info = XLOG_BRIN_UPDATE | (extended ? XLOG_BRIN_INIT_PAGE : 0);
+
+			xlrec.insert.offnum = newoff;
+			xlrec.insert.heapBlk = heapBlk;
+			xlrec.insert.pagesPerRange = pagesPerRange;
+			xlrec.oldOffnum = oldoff;
+
+			XLogBeginInsert();
+
+			/* new page */
+			XLogRegisterData((char *) &xlrec, SizeOfBrinUpdate);
+
+			XLogRegisterBuffer(0, newbuf, REGBUF_STANDARD | (extended ? REGBUF_WILL_INIT : 0));
+			XLogRegisterBufData(0, (char *) unconstify(BrinTuple *, newtup), newsz);
+
+			/* revmap page */
+			XLogRegisterBuffer(1, revmapbuf, 0);
+
+			/* old page */
+			XLogRegisterBuffer(2, oldbuf, REGBUF_STANDARD);
+
+			recptr = XLogInsert(RM_BRIN_ID, info);
+
+			PageSetLSN(oldpage, recptr);
+			PageSetLSN(newpage, recptr);
+			PageSetLSN(BufferGetPage(revmapbuf), recptr);
+		}
+
+		END_CRIT_SECTION();
+
+		LockBuffer(revmapbuf, BUFFER_LOCK_UNLOCK);
+		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
+		UnlockReleaseBuffer(newbuf);
+
+		if (extended)
+		{
+			RecordPageWithFreeSpace(idxrel, newblk, freespace);
+			FreeSpaceMapVacuumRange(idxrel, newblk, newblk + 1);
+		}
+
+		return true;
+	}
+}
+
+/*
+ * Return whether brin_doupdate can do a samepage update.
+ */
+bool
+brin_can_do_samepage_update(Buffer buffer, Size origsz, Size newsz)
+{
+	return
+		((newsz <= origsz) ||
+		 PageGetExactFreeSpace(BufferGetPage(buffer)) >= (newsz - origsz));
+}
+
+/*
+ * Insert an index tuple into the index relation.  The revmap is updated to
+ * mark the range containing the given page as pointing to the inserted entry.
+ * A WAL record is written.
+ *
+ * The buffer, if valid, is first checked for free space to insert the new
+ * entry; if there isn't enough, a new buffer is obtained and pinned.  No
+ * buffer lock must be held on entry, no buffer lock is held on exit.
+ *
+ * Return value is the offset number where the tuple was inserted.
+ */
+OffsetNumber
+brin_doinsert(Relation idxrel, BlockNumber pagesPerRange,
+			  BrinRevmap *revmap, Buffer *buffer, BlockNumber heapBlk,
+			  BrinTuple *tup, Size itemsz)
+{
+	Page		page;
+	BlockNumber blk;
+	OffsetNumber off;
+	Size		freespace = 0;
+	Buffer		revmapbuf;
+	ItemPointerData tid;
+	bool		extended;
+
+	Assert(itemsz == MAXALIGN(itemsz));
+
+	/* If the item is oversized, don't even bother. */
+	if (itemsz > BrinMaxItemSize)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("index row size %zu exceeds maximum %zu for index \"%s\"",
+						itemsz, BrinMaxItemSize, RelationGetRelationName(idxrel))));
+		return InvalidOffsetNumber; /* keep compiler quiet */
+	}
+
+	/* Make sure the revmap is long enough to contain the entry we need */
+	brinRevmapExtend(revmap, heapBlk);
+
+	/*
+	 * Acquire lock on buffer supplied by caller, if any.  If it doesn't have
+	 * enough space, unpin it to obtain a new one below.
+	 */
+	if (BufferIsValid(*buffer))
+	{
+		/*
+		 * It's possible that another backend (or ourselves!) extended the
+		 * revmap over the page we held a pin on, so we cannot assume that
+		 * it's still a regular page.
+		 */
+		LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
+		if (br_page_get_freespace(BufferGetPage(*buffer)) < itemsz)
+		{
+			UnlockReleaseBuffer(*buffer);
+			*buffer = InvalidBuffer;
+		}
+	}
+
+	/*
+	 * If we still don't have a usable buffer, have brin_getinsertbuffer
+	 * obtain one for us.
+	 */
+	if (!BufferIsValid(*buffer))
+	{
+		do
+			*buffer = brin_getinsertbuffer(idxrel, InvalidBuffer, itemsz, &extended);
+		while (!BufferIsValid(*buffer));
+	}
+	else
+		extended = false;
+
+	/* Now obtain lock on revmap buffer */
+	revmapbuf = brinLockRevmapPageForUpdate(revmap, heapBlk);
+
+	page = BufferGetPage(*buffer);
+	blk = BufferGetBlockNumber(*buffer);
+
+	/* Execute the actual insertion */
+	START_CRIT_SECTION();
+	if (extended)
+		brin_page_init(page, BRIN_PAGETYPE_REGULAR);
+	off = PageAddItem(page, (Item) tup, itemsz, InvalidOffsetNumber,
+					  false, false);
+	if (off == InvalidOffsetNumber)
+		elog(ERROR, "failed to add BRIN tuple to new page");
+	MarkBufferDirty(*buffer);
+
+	/* needed to update FSM below */
+	if (extended)
+		freespace = br_page_get_freespace(page);
+
+	ItemPointerSet(&tid, blk, off);
+	brinSetHeapBlockItemptr(revmapbuf, pagesPerRange, heapBlk, tid);
+	MarkBufferDirty(revmapbuf);
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(idxrel))
+	{
+		xl_brin_insert xlrec;
+		XLogRecPtr	recptr;
+		uint8		info;
+
+		info = XLOG_BRIN_INSERT | (extended ? XLOG_BRIN_INIT_PAGE : 0);
+		xlrec.heapBlk = heapBlk;
+		xlrec.pagesPerRange = pagesPerRange;
+		xlrec.offnum = off;
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) &xlrec, SizeOfBrinInsert);
+
+		XLogRegisterBuffer(0, *buffer, REGBUF_STANDARD | (extended ? REGBUF_WILL_INIT : 0));
+		XLogRegisterBufData(0, (char *) tup, itemsz);
+
+		XLogRegisterBuffer(1, revmapbuf, 0);
+
+		recptr = XLogInsert(RM_BRIN_ID, info);
+
+		PageSetLSN(page, recptr);
+		PageSetLSN(BufferGetPage(revmapbuf), recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	/* Tuple is firmly on buffer; we can release our locks */
+	LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
+	LockBuffer(revmapbuf, BUFFER_LOCK_UNLOCK);
+
+	BRIN_elog((DEBUG2, "inserted tuple (%u,%u) for range starting at %u",
+			   blk, off, heapBlk));
+
+	if (extended)
+	{
+		RecordPageWithFreeSpace(idxrel, blk, freespace);
+		FreeSpaceMapVacuumRange(idxrel, blk, blk + 1);
+	}
+
+	return off;
+}
+
+/*
+ * Initialize a page with the given type.
+ *
+ * Caller is responsible for marking it dirty, as appropriate.
+ */
+void
+brin_page_init(Page page, uint16 type)
+{
+	PageInit(page, BLCKSZ, sizeof(BrinSpecialSpace));
+
+	BrinPageType(page) = type;
+}
+
+/*
+ * Initialize a new BRIN index's metapage.
+ */
+void
+brin_metapage_init(Page page, BlockNumber pagesPerRange, uint16 version)
+{
+	BrinMetaPageData *metadata;
+
+	brin_page_init(page, BRIN_PAGETYPE_META);
+
+	metadata = (BrinMetaPageData *) PageGetContents(page);
+
+	metadata->brinMagic = BRIN_META_MAGIC;
+	metadata->brinVersion = version;
+	metadata->pagesPerRange = pagesPerRange;
+
+	/*
+	 * Note we cheat here a little.  0 is not a valid revmap block number
+	 * (because it's the metapage buffer), but doing this enables the first
+	 * revmap page to be created when the index is.
+	 */
+	metadata->lastRevmapPage = 0;
+
+	/*
+	 * Set pd_lower just past the end of the metadata.  This is essential,
+	 * because without doing so, metadata will be lost if xlog.c compresses
+	 * the page.
+	 */
+	((PageHeader) page)->pd_lower =
+		((char *) metadata + sizeof(BrinMetaPageData)) - (char *) page;
+}
+
+/*
+ * Initiate page evacuation protocol.
+ *
+ * The page must be locked in exclusive mode by the caller.
+ *
+ * If the page is not yet initialized or empty, return false without doing
+ * anything; it can be used for revmap without any further changes.  If it
+ * contains tuples, mark it for evacuation and return true.
+ */
+bool
+brin_start_evacuating_page(Relation idxRel, Buffer buf)
+{
+	OffsetNumber off;
+	OffsetNumber maxoff;
+	Page		page;
+
+	page = BufferGetPage(buf);
+
+	if (PageIsNew(page))
+		return false;
+
+	maxoff = PageGetMaxOffsetNumber(page);
+	for (off = FirstOffsetNumber; off <= maxoff; off++)
+	{
+		ItemId		lp;
+
+		lp = PageGetItemId(page, off);
+		if (ItemIdIsUsed(lp))
+		{
+			/*
+			 * Prevent other backends from adding more stuff to this page:
+			 * BRIN_EVACUATE_PAGE informs br_page_get_freespace that this page
+			 * can no longer be used to add new tuples.  Note that this flag
+			 * is not WAL-logged, except accidentally.
+			 */
+			BrinPageFlags(page) |= BRIN_EVACUATE_PAGE;
+			MarkBufferDirtyHint(buf, true);
+
+			return true;
+		}
+	}
+	return false;
+}
+
+/*
+ * Move all tuples out of a page.
+ *
+ * The caller must hold lock on the page. The lock and pin are released.
+ */
+void
+brin_evacuate_page(Relation idxRel, BlockNumber pagesPerRange,
+				   BrinRevmap *revmap, Buffer buf)
+{
+	OffsetNumber off;
+	OffsetNumber maxoff;
+	Page		page;
+	BrinTuple  *btup = NULL;
+	Size		btupsz = 0;
+
+	page = BufferGetPage(buf);
+
+	Assert(BrinPageFlags(page) & BRIN_EVACUATE_PAGE);
+
+	maxoff = PageGetMaxOffsetNumber(page);
+	for (off = FirstOffsetNumber; off <= maxoff; off++)
+	{
+		BrinTuple  *tup;
+		Size		sz;
+		ItemId		lp;
+
+		CHECK_FOR_INTERRUPTS();
+
+		lp = PageGetItemId(page, off);
+		if (ItemIdIsUsed(lp))
+		{
+			sz = ItemIdGetLength(lp);
+			tup = (BrinTuple *) PageGetItem(page, lp);
+			tup = brin_copy_tuple(tup, sz, btup, &btupsz);
+
+			LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+
+			if (!brin_doupdate(idxRel, pagesPerRange, revmap, tup->bt_blkno,
+							   buf, off, tup, sz, tup, sz, false))
+				off--;			/* retry */
+
+			LockBuffer(buf, BUFFER_LOCK_SHARE);
+
+			/* It's possible that someone extended the revmap over this page */
+			if (!BRIN_IS_REGULAR_PAGE(page))
+				break;
+		}
+	}
+
+	UnlockReleaseBuffer(buf);
+}
+
+/*
+ * Given a BRIN index page, initialize it if necessary, and record its
+ * current free space in the FSM.
+ *
+ * The main use for this is when, during vacuuming, an uninitialized page is
+ * found, which could be the result of relation extension followed by a crash
+ * before the page can be used.
+ *
+ * Here, we don't bother to update upper FSM pages, instead expecting that our
+ * caller (brin_vacuum_scan) will fix them at the end of the scan.  Elsewhere
+ * in this file, it's generally a good idea to propagate additions of free
+ * space into the upper FSM pages immediately.
+ */
+void
+brin_page_cleanup(Relation idxrel, Buffer buf)
+{
+	Page		page = BufferGetPage(buf);
+
+	/*
+	 * If a page was left uninitialized, initialize it now; also record it in
+	 * FSM.
+	 *
+	 * Somebody else might be extending the relation concurrently.  To avoid
+	 * re-initializing the page before they can grab the buffer lock, we
+	 * acquire the extension lock momentarily.  Since they hold the extension
+	 * lock from before getting the page and after its been initialized, we're
+	 * sure to see their initialization.
+	 */
+	if (PageIsNew(page))
+	{
+		LockRelationForExtension(idxrel, ShareLock);
+		UnlockRelationForExtension(idxrel, ShareLock);
+
+		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+		if (PageIsNew(page))
+		{
+			brin_initialize_empty_new_buffer(idxrel, buf);
+			LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+			return;
+		}
+		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+	}
+
+	/* Nothing to be done for non-regular index pages */
+	if (BRIN_IS_META_PAGE(BufferGetPage(buf)) ||
+		BRIN_IS_REVMAP_PAGE(BufferGetPage(buf)))
+		return;
+
+	/* Measure free space and record it */
+	RecordPageWithFreeSpace(idxrel, BufferGetBlockNumber(buf),
+							br_page_get_freespace(page));
+}
+
+/*
+ * Return a pinned and exclusively locked buffer which can be used to insert an
+ * index item of size itemsz (caller must ensure not to request sizes
+ * impossible to fulfill).  If oldbuf is a valid buffer, it is also locked (in
+ * an order determined to avoid deadlocks).
+ *
+ * If we find that the old page is no longer a regular index page (because
+ * of a revmap extension), the old buffer is unlocked and we return
+ * InvalidBuffer.
+ *
+ * If there's no existing page with enough free space to accommodate the new
+ * item, the relation is extended.  If this happens, *extended is set to true,
+ * and it is the caller's responsibility to initialize the page (and WAL-log
+ * that fact) prior to use.  The caller should also update the FSM with the
+ * page's remaining free space after the insertion.
+ *
+ * Note that the caller is not expected to update FSM unless *extended is set
+ * true.  This policy means that we'll update FSM when a page is created, and
+ * when it's found to have too little space for a desired tuple insertion,
+ * but not every single time we add a tuple to the page.
+ *
+ * Note that in some corner cases it is possible for this routine to extend
+ * the relation and then not return the new page.  It is this routine's
+ * responsibility to WAL-log the page initialization and to record the page in
+ * FSM if that happens, since the caller certainly can't do it.
+ */
+static Buffer
+brin_getinsertbuffer(Relation irel, Buffer oldbuf, Size itemsz,
+					 bool *extended)
+{
+	BlockNumber oldblk;
+	BlockNumber newblk;
+	Page		page;
+	Size		freespace;
+
+	/* callers must have checked */
+	Assert(itemsz <= BrinMaxItemSize);
+
+	if (BufferIsValid(oldbuf))
+		oldblk = BufferGetBlockNumber(oldbuf);
+	else
+		oldblk = InvalidBlockNumber;
+
+	/* Choose initial target page, re-using existing target if known */
+	newblk = RelationGetTargetBlock(irel);
+	if (newblk == InvalidBlockNumber)
+		newblk = GetPageWithFreeSpace(irel, itemsz);
+
+	/*
+	 * Loop until we find a page with sufficient free space.  By the time we
+	 * return to caller out of this loop, both buffers are valid and locked;
+	 * if we have to restart here, neither page is locked and newblk isn't
+	 * pinned (if it's even valid).
+	 */
+	for (;;)
+	{
+		Buffer		buf;
+		bool		extensionLockHeld = false;
+
+		CHECK_FOR_INTERRUPTS();
+
+		*extended = false;
+
+		if (newblk == InvalidBlockNumber)
+		{
+			/*
+			 * There's not enough free space in any existing index page,
+			 * according to the FSM: extend the relation to obtain a shiny new
+			 * page.
+			 */
+			if (!RELATION_IS_LOCAL(irel))
+			{
+				LockRelationForExtension(irel, ExclusiveLock);
+				extensionLockHeld = true;
+			}
+			buf = ReadBuffer(irel, P_NEW);
+			newblk = BufferGetBlockNumber(buf);
+			*extended = true;
+
+			BRIN_elog((DEBUG2, "brin_getinsertbuffer: extending to page %u",
+					   BufferGetBlockNumber(buf)));
+		}
+		else if (newblk == oldblk)
+		{
+			/*
+			 * There's an odd corner-case here where the FSM is out-of-date,
+			 * and gave us the old page.
+			 */
+			buf = oldbuf;
+		}
+		else
+		{
+			buf = ReadBuffer(irel, newblk);
+		}
+
+		/*
+		 * We lock the old buffer first, if it's earlier than the new one; but
+		 * then we need to check that it hasn't been turned into a revmap page
+		 * concurrently.  If we detect that that happened, give up and tell
+		 * caller to start over.
+		 */
+		if (BufferIsValid(oldbuf) && oldblk < newblk)
+		{
+			LockBuffer(oldbuf, BUFFER_LOCK_EXCLUSIVE);
+			if (!BRIN_IS_REGULAR_PAGE(BufferGetPage(oldbuf)))
+			{
+				LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
+
+				/*
+				 * It is possible that the new page was obtained from
+				 * extending the relation.  In that case, we must be sure to
+				 * record it in the FSM before leaving, because otherwise the
+				 * space would be lost forever.  However, we cannot let an
+				 * uninitialized page get in the FSM, so we need to initialize
+				 * it first.
+				 */
+				if (*extended)
+					brin_initialize_empty_new_buffer(irel, buf);
+
+				if (extensionLockHeld)
+					UnlockRelationForExtension(irel, ExclusiveLock);
+
+				ReleaseBuffer(buf);
+
+				if (*extended)
+				{
+					FreeSpaceMapVacuumRange(irel, newblk, newblk + 1);
+					/* shouldn't matter, but don't confuse caller */
+					*extended = false;
+				}
+
+				return InvalidBuffer;
+			}
+		}
+
+		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+
+		if (extensionLockHeld)
+			UnlockRelationForExtension(irel, ExclusiveLock);
+
+		page = BufferGetPage(buf);
+
+		/*
+		 * We have a new buffer to insert into.  Check that the new page has
+		 * enough free space, and return it if it does; otherwise start over.
+		 * (br_page_get_freespace also checks that the FSM didn't hand us a
+		 * page that has since been repurposed for the revmap.)
+		 */
+		freespace = *extended ?
+			BrinMaxItemSize : br_page_get_freespace(page);
+		if (freespace >= itemsz)
+		{
+			RelationSetTargetBlock(irel, newblk);
+
+			/*
+			 * Lock the old buffer if not locked already.  Note that in this
+			 * case we know for sure it's a regular page: it's later than the
+			 * new page we just got, which is not a revmap page, and revmap
+			 * pages are always consecutive.
+			 */
+			if (BufferIsValid(oldbuf) && oldblk > newblk)
+			{
+				LockBuffer(oldbuf, BUFFER_LOCK_EXCLUSIVE);
+				Assert(BRIN_IS_REGULAR_PAGE(BufferGetPage(oldbuf)));
+			}
+
+			return buf;
+		}
+
+		/* This page is no good. */
+
+		/*
+		 * If an entirely new page does not contain enough free space for the
+		 * new item, then surely that item is oversized.  Complain loudly; but
+		 * first make sure we initialize the page and record it as free, for
+		 * next time.
+		 */
+		if (*extended)
+		{
+			brin_initialize_empty_new_buffer(irel, buf);
+			/* since this should not happen, skip FreeSpaceMapVacuum */
+
+			ereport(ERROR,
+					(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+					 errmsg("index row size %zu exceeds maximum %zu for index \"%s\"",
+							itemsz, freespace, RelationGetRelationName(irel))));
+			return InvalidBuffer;	/* keep compiler quiet */
+		}
+
+		if (newblk != oldblk)
+			UnlockReleaseBuffer(buf);
+		if (BufferIsValid(oldbuf) && oldblk <= newblk)
+			LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
+
+		/*
+		 * Update the FSM with the new, presumably smaller, freespace value
+		 * for this page, then search for a new target page.
+		 */
+		newblk = RecordAndGetPageWithFreeSpace(irel, newblk, freespace, itemsz);
+	}
+}
+
+/*
+ * Initialize a page as an empty regular BRIN page, WAL-log this, and record
+ * the page in FSM.
+ *
+ * There are several corner situations in which we extend the relation to
+ * obtain a new page and later find that we cannot use it immediately.  When
+ * that happens, we don't want to leave the page go unrecorded in FSM, because
+ * there is no mechanism to get the space back and the index would bloat.
+ * Also, because we would not WAL-log the action that would initialize the
+ * page, the page would go uninitialized in a standby (or after recovery).
+ *
+ * While we record the page in FSM here, caller is responsible for doing FSM
+ * upper-page update if that seems appropriate.
+ */
+static void
+brin_initialize_empty_new_buffer(Relation idxrel, Buffer buffer)
+{
+	Page		page;
+
+	BRIN_elog((DEBUG2,
+			   "brin_initialize_empty_new_buffer: initializing blank page %u",
+			   BufferGetBlockNumber(buffer)));
+
+	START_CRIT_SECTION();
+	page = BufferGetPage(buffer);
+	brin_page_init(page, BRIN_PAGETYPE_REGULAR);
+	MarkBufferDirty(buffer);
+	log_newpage_buffer(buffer, true);
+	END_CRIT_SECTION();
+
+	/*
+	 * We update the FSM for this page, but this is not WAL-logged.  This is
+	 * acceptable because VACUUM will scan the index and update the FSM with
+	 * pages whose FSM records were forgotten in a crash.
+	 */
+	RecordPageWithFreeSpace(idxrel, BufferGetBlockNumber(buffer),
+							br_page_get_freespace(page));
+}
+
+
+/*
+ * Return the amount of free space on a regular BRIN index page.
+ *
+ * If the page is not a regular page, or has been marked with the
+ * BRIN_EVACUATE_PAGE flag, returns 0.
+ */
+static Size
+br_page_get_freespace(Page page)
+{
+	if (!BRIN_IS_REGULAR_PAGE(page) ||
+		(BrinPageFlags(page) & BRIN_EVACUATE_PAGE) != 0)
+		return 0;
+	else
+		return PageGetFreeSpace(page);
+}