Predicate locking in GIN index

Predicate locks are used on per page basis only if fastupdate = off, in
opposite case predicate lock on pending list will effectively lock whole index,
to reduce locking overhead, just lock a relation. Entry and posting trees are
essentially B-tree, so locks are acquired on leaf pages only.

Author: Shubham Barai with some editorization by me and Dmitry Ivanov
Review by: Alexander Korotkov, Dmitry Ivanov, Fedor Sigaev
Discussion: https://www.postgresql.org/message-id/flat/CALxAEPt5sWW+EwTaKUGFL5_XFcZ0MuGBcyJ70oqbWqr42YKR8Q@mail.gmail.com

Author: feodor

src/backend/access/gin/ginbtree.c

@@ -17,6 +17,7 @@
 #include "access/gin_private.h"
 #include "access/ginxlog.h"
 #include "access/xloginsert.h"
+#include "storage/predicate.h"
 #include "miscadmin.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
@@ -515,6 +516,19 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
 			btree->fillRoot(btree, newrootpg,
 							BufferGetBlockNumber(lbuffer), newlpage,
 							BufferGetBlockNumber(rbuffer), newrpage);
+
+			if (GinPageIsLeaf(BufferGetPage(stack->buffer)))
+			{
+
+				PredicateLockPageSplit(btree->index,
+						BufferGetBlockNumber(stack->buffer),
+						BufferGetBlockNumber(lbuffer));
+
+				PredicateLockPageSplit(btree->index,
+						BufferGetBlockNumber(stack->buffer),
+						BufferGetBlockNumber(rbuffer));
+			}
+
 		}
 		else
 		{
@@ -524,6 +538,14 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
 			GinPageGetOpaque(newrpage)->rightlink = savedRightLink;
 			GinPageGetOpaque(newlpage)->flags |= GIN_INCOMPLETE_SPLIT;
 			GinPageGetOpaque(newlpage)->rightlink = BufferGetBlockNumber(rbuffer);
+
+			if (GinPageIsLeaf(BufferGetPage(stack->buffer)))
+			{
+
+				PredicateLockPageSplit(btree->index,
+						BufferGetBlockNumber(stack->buffer),
+						BufferGetBlockNumber(rbuffer));
+			}
 		}
 
 		/*

src/backend/access/gin/gindatapage.c

@@ -19,6 +19,7 @@
 #include "access/xloginsert.h"
 #include "lib/ilist.h"
 #include "miscadmin.h"
+#include "storage/predicate.h"
 #include "utils/rel.h"
 
 /*
@@ -1759,7 +1760,7 @@ leafRepackItems(disassembledLeaf *leaf, ItemPointer remaining)
  */
 BlockNumber
 createPostingTree(Relation index, ItemPointerData *items, uint32 nitems,
-				  GinStatsData *buildStats)
+				  GinStatsData *buildStats, Buffer entrybuffer)
 {
 	BlockNumber blkno;
 	Buffer		buffer;
@@ -1810,6 +1811,12 @@ createPostingTree(Relation index, ItemPointerData *items, uint32 nitems,
 	page = BufferGetPage(buffer);
 	blkno = BufferGetBlockNumber(buffer);
 
+	/*
+	 * Copy a predicate lock from entry tree leaf (containing posting list)
+	 * to  posting tree.
+	 */
+	PredicateLockPageSplit(index, BufferGetBlockNumber(entrybuffer), blkno);
+
 	START_CRIT_SECTION();
 
 	PageRestoreTempPage(tmppage, page);
@@ -1904,6 +1911,7 @@ ginInsertItemPointers(Relation index, BlockNumber rootBlkno,
 		btree.itemptr = insertdata.items[insertdata.curitem];
 		stack = ginFindLeafPage(&btree, false, NULL);
 
+		GinCheckForSerializableConflictIn(btree.index, NULL, stack->buffer);
 		ginInsertValue(&btree, stack, &insertdata, buildStats);
 	}
 }

src/backend/access/gin/ginget.c

@@ -17,8 +17,10 @@
 #include "access/gin_private.h"
 #include "access/relscan.h"
 #include "miscadmin.h"
+#include "storage/predicate.h"
 #include "utils/datum.h"
 #include "utils/memutils.h"
+#include "utils/rel.h"
 
 /* GUC parameter */
 int			GinFuzzySearchLimit = 0;
@@ -33,11 +35,25 @@ typedef struct pendingPosition
 } pendingPosition;
 
 
+/*
+ * Place predicate lock on GIN page if needed.
+ */
+static void
+GinPredicateLockPage(Relation index, BlockNumber blkno, Snapshot snapshot)
+{
+	/*
+	 * When fast update is on then no need in locking pages, because we
+	 * anyway need to lock the whole index.
+	 */
+	if (!GinGetUseFastUpdate(index))
+			PredicateLockPage(index, blkno, snapshot);
+}
+
 /*
  * Goes to the next page if current offset is outside of bounds
  */
 static bool
-moveRightIfItNeeded(GinBtreeData *btree, GinBtreeStack *stack)
+moveRightIfItNeeded(GinBtreeData *btree, GinBtreeStack *stack, Snapshot snapshot)
 {
 	Page		page = BufferGetPage(stack->buffer);
 
@@ -52,6 +68,7 @@ moveRightIfItNeeded(GinBtreeData *btree, GinBtreeStack *stack)
 		stack->buffer = ginStepRight(stack->buffer, btree->index, GIN_SHARE);
 		stack->blkno = BufferGetBlockNumber(stack->buffer);
 		stack->off = FirstOffsetNumber;
+		GinPredicateLockPage(btree->index, stack->blkno, snapshot);
 	}
 
 	return true;
@@ -73,6 +90,7 @@ scanPostingTree(Relation index, GinScanEntry scanEntry,
 	/* Descend to the leftmost leaf page */
 	stack = ginScanBeginPostingTree(&btree, index, rootPostingTree, snapshot);
 	buffer = stack->buffer;
+
 	IncrBufferRefCount(buffer); /* prevent unpin in freeGinBtreeStack */
 
 	freeGinBtreeStack(stack);
@@ -82,6 +100,11 @@ scanPostingTree(Relation index, GinScanEntry scanEntry,
 	 */
 	for (;;)
 	{
+		/*
+		 * Predicate lock each leaf page in posting tree
+		 */
+		GinPredicateLockPage(index, BufferGetBlockNumber(buffer), snapshot);
+
 		page = BufferGetPage(buffer);
 		if ((GinPageGetOpaque(page)->flags & GIN_DELETED) == 0)
 		{
@@ -131,6 +154,12 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
 	attnum = scanEntry->attnum;
 	attr = TupleDescAttr(btree->ginstate->origTupdesc, attnum - 1);
 
+	/*
+	 * Predicate lock entry leaf page, following pages will be locked by
+	 * moveRightIfItNeeded()
+	 */
+	GinPredicateLockPage(btree->index, stack->buffer, snapshot);
+
 	for (;;)
 	{
 		Page		page;
@@ -141,7 +170,7 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
 		/*
 		 * stack->off points to the interested entry, buffer is already locked
 		 */
-		if (moveRightIfItNeeded(btree, stack) == false)
+		if (moveRightIfItNeeded(btree, stack, snapshot) == false)
 			return true;
 
 		page = BufferGetPage(stack->buffer);
@@ -250,7 +279,7 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
 				Datum		newDatum;
 				GinNullCategory newCategory;
 
-				if (moveRightIfItNeeded(btree, stack) == false)
+				if (moveRightIfItNeeded(btree, stack, snapshot) == false)
 					elog(ERROR, "lost saved point in index");	/* must not happen !!! */
 
 				page = BufferGetPage(stack->buffer);
@@ -323,6 +352,7 @@ startScanEntry(GinState *ginstate, GinScanEntry entry, Snapshot snapshot)
 						ginstate);
 	stackEntry = ginFindLeafPage(&btreeEntry, true, snapshot);
 	page = BufferGetPage(stackEntry->buffer);
+
 	/* ginFindLeafPage() will have already checked snapshot age. */
 	needUnlock = true;
 
@@ -370,6 +400,10 @@ startScanEntry(GinState *ginstate, GinScanEntry entry, Snapshot snapshot)
 	{
 		IndexTuple	itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, stackEntry->off));
 
+		/* Predicate lock visited entry leaf page */
+		GinPredicateLockPage(ginstate->index,
+							 BufferGetBlockNumber(stackEntry->buffer), snapshot);
+
 		if (GinIsPostingTree(itup))
 		{
 			BlockNumber rootPostingTree = GinGetPostingTree(itup);
@@ -391,6 +425,12 @@ startScanEntry(GinState *ginstate, GinScanEntry entry, Snapshot snapshot)
 											rootPostingTree, snapshot);
 			entry->buffer = stack->buffer;
 
+			/*
+			 * Predicate lock visited posting tree page, following pages
+			 * will be locked by moveRightIfItNeeded or entryLoadMoreItems
+			 */
+			GinPredicateLockPage(ginstate->index, BufferGetBlockNumber(entry->buffer), snapshot);
+
 			/*
 			 * We keep buffer pinned because we need to prevent deletion of
 			 * page during scan. See GIN's vacuum implementation. RefCount is
@@ -493,7 +533,7 @@ startScanKey(GinState *ginstate, GinScanOpaque so, GinScanKey key)
 
 		for (i = 0; i < key->nentries - 1; i++)
 		{
-			/* Pass all entries <= i as FALSE, and the rest as MAYBE */
+			/* Pass all entries <= i as false, and the rest as MAYBE */
 			for (j = 0; j <= i; j++)
 				key->entryRes[entryIndexes[j]] = GIN_FALSE;
 			for (j = i + 1; j < key->nentries; j++)
@@ -633,6 +673,8 @@ entryLoadMoreItems(GinState *ginstate, GinScanEntry entry,
 		entry->btree.fullScan = false;
 		stack = ginFindLeafPage(&entry->btree, true, snapshot);
 
+		GinPredicateLockPage(ginstate->index, BufferGetBlockNumber(stack->buffer), snapshot);
+
 		/* we don't need the stack, just the buffer. */
 		entry->buffer = stack->buffer;
 		IncrBufferRefCount(entry->buffer);
@@ -677,6 +719,10 @@ entryLoadMoreItems(GinState *ginstate, GinScanEntry entry,
 			entry->buffer = ginStepRight(entry->buffer,
 										 ginstate->index,
 										 GIN_SHARE);
+
+			GinPredicateLockPage(ginstate->index, BufferGetBlockNumber(entry->buffer), snapshot);
+
+
 			page = BufferGetPage(entry->buffer);
 		}
 		stepright = true;
@@ -1038,8 +1084,8 @@ keyGetItem(GinState *ginstate, MemoryContext tempCtx, GinScanKey key,
 	 * lossy page even when none of the other entries match.
 	 *
 	 * Our strategy is to call the tri-state consistent function, with the
-	 * lossy-page entries set to MAYBE, and all the other entries FALSE. If it
-	 * returns FALSE, none of the lossy items alone are enough for a match, so
+	 * lossy-page entries set to MAYBE, and all the other entries false. If it
+	 * returns false, none of the lossy items alone are enough for a match, so
 	 * we don't need to return a lossy-page pointer. Otherwise, return a
 	 * lossy-page pointer to indicate that the whole heap page must be
 	 * checked.  (On subsequent calls, we'll do nothing until minItem is past
@@ -1700,7 +1746,8 @@ collectMatchesForHeapRow(IndexScanDesc scan, pendingPosition *pos)
 }
 
 /*
- * Collect all matched rows from pending list into bitmap
+ * Collect all matched rows from pending list into bitmap. Also function
+ * takes PendingLockRelation if it's needed.
  */
 static void
 scanPendingInsert(IndexScanDesc scan, TIDBitmap *tbm, int64 *ntids)
@@ -1730,9 +1777,24 @@ scanPendingInsert(IndexScanDesc scan, TIDBitmap *tbm, int64 *ntids)
 	{
 		/* No pending list, so proceed with normal scan */
 		UnlockReleaseBuffer(metabuffer);
+
+		/*
+		 * If fast update is enabled, we acquire a predicate lock on the entire
+		 * relation as fast update postpones the insertion of tuples into index
+		 * structure due to which we can't detect rw conflicts.
+		 */
+		if (GinGetUseFastUpdate(scan->indexRelation))
+			PredicateLockRelation(scan->indexRelation, scan->xs_snapshot);
+
 		return;
 	}
 
+	/*
+	 * Pending list is not empty, we need to lock the index doesn't despite on
+	 * fastupdate state
+	 */
+	PredicateLockRelation(scan->indexRelation, scan->xs_snapshot);
+
 	pos.pendingBuffer = ReadBuffer(scan->indexRelation, blkno);
 	LockBuffer(pos.pendingBuffer, GIN_SHARE);
 	pos.firstOffset = FirstOffsetNumber;

src/backend/access/gin/gininsert.c

@@ -22,6 +22,7 @@
 #include "storage/bufmgr.h"
 #include "storage/smgr.h"
 #include "storage/indexfsm.h"
+#include "storage/predicate.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 
@@ -48,7 +49,7 @@ static IndexTuple
 addItemPointersToLeafTuple(GinState *ginstate,
 						   IndexTuple old,
 						   ItemPointerData *items, uint32 nitem,
-						   GinStatsData *buildStats)
+						   GinStatsData *buildStats, Buffer buffer)
 {
 	OffsetNumber attnum;
 	Datum		key;
@@ -99,7 +100,8 @@ addItemPointersToLeafTuple(GinState *ginstate,
 		postingRoot = createPostingTree(ginstate->index,
 										oldItems,
 										oldNPosting,
-										buildStats);
+										buildStats,
+										buffer);
 
 		/* Now insert the TIDs-to-be-added into the posting tree */
 		ginInsertItemPointers(ginstate->index, postingRoot,
@@ -127,7 +129,7 @@ static IndexTuple
 buildFreshLeafTuple(GinState *ginstate,
 					OffsetNumber attnum, Datum key, GinNullCategory category,
 					ItemPointerData *items, uint32 nitem,
-					GinStatsData *buildStats)
+					GinStatsData *buildStats, Buffer buffer)
 {
 	IndexTuple	res = NULL;
 	GinPostingList *compressedList;
@@ -157,7 +159,7 @@ buildFreshLeafTuple(GinState *ginstate,
 		 * Initialize a new posting tree with the TIDs.
 		 */
 		postingRoot = createPostingTree(ginstate->index, items, nitem,
-										buildStats);
+										buildStats, buffer);
 
 		/* And save the root link in the result tuple */
 		GinSetPostingTree(res, postingRoot);
@@ -217,17 +219,19 @@ ginEntryInsert(GinState *ginstate,
 			return;
 		}
 
+		GinCheckForSerializableConflictIn(btree.index, NULL, stack->buffer);
 		/* modify an existing leaf entry */
 		itup = addItemPointersToLeafTuple(ginstate, itup,
-										  items, nitem, buildStats);
+										  items, nitem, buildStats, stack->buffer);
 
 		insertdata.isDelete = true;
 	}
 	else
 	{
+		GinCheckForSerializableConflictIn(btree.index, NULL, stack->buffer);
 		/* no match, so construct a new leaf entry */
 		itup = buildFreshLeafTuple(ginstate, attnum, key, category,
-								   items, nitem, buildStats);
+								   items, nitem, buildStats, stack->buffer);
 	}
 
 	/* Insert the new or modified leaf tuple */
@@ -513,6 +517,18 @@ gininsert(Relation index, Datum *values, bool *isnull,
 
 		memset(&collector, 0, sizeof(GinTupleCollector));
 
+		/*
+		 * With fastupdate on each scan and each insert begin with access to
+		 * pending list, so it effectively lock entire index. In this case
+		 * we aquire predicate lock and check for conflicts over index relation,
+		 * and hope that it will reduce locking overhead.
+		 *
+		 * Do not use GinCheckForSerializableConflictIn() here, because
+		 * it will do nothing (it does actual work only with fastupdate off).
+		 * Check for conflicts for entire index.
+		 */
+		CheckForSerializableConflictIn(index, NULL, InvalidBuffer);
+
 		for (i = 0; i < ginstate->origTupdesc->natts; i++)
 			ginHeapTupleFastCollect(ginstate, &collector,
 									(OffsetNumber) (i + 1),
@@ -523,6 +539,16 @@ gininsert(Relation index, Datum *values, bool *isnull,
 	}
 	else
 	{
+		GinStatsData	stats;
+
+		/*
+		 * Fastupdate is off but if pending list isn't empty then we need to
+		 * check conflicts with PredicateLockRelation in scanPendingInsert().
+		 */
+		ginGetStats(index, &stats);
+		if (stats.nPendingPages > 0)
+			CheckForSerializableConflictIn(index, NULL, InvalidBuffer);
+
 		for (i = 0; i < ginstate->origTupdesc->natts; i++)
 			ginHeapTupleInsert(ginstate, (OffsetNumber) (i + 1),
 							   values[i], isnull[i],