Fix possible duplicate tuples while GiST scan. Now page is processed

at once and ItemPointers are collected in memory.

Remove tuple's killing by killtuple() if tuple was moved to another
page - it could produce unaceptable overhead.

Backpatch up to 8.1 because the bug was introduced by GiST's concurrency support.

src/backend/access/gist/gistget.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/gist/gistget.c,v 1.74 2008/06/19 00:46:03 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gistget.c,v 1.75 2008/08/23 10:37:24 teodor Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -32,63 +32,39 @@ static bool gistindex_keytest(IndexTuple tuple, IndexScanDesc scan,
 static void
 killtuple(Relation r, GISTScanOpaque so, ItemPointer iptr)
 {
-	Buffer		buffer = so->curbuf;
-
-	for (;;)
-	{
-		Page		p;
-		BlockNumber blkno;
-		OffsetNumber offset,
-					maxoff;
-
-		LockBuffer(buffer, GIST_SHARE);
-		gistcheckpage(r, buffer);
-		p = (Page) BufferGetPage(buffer);
+	Page		p;
+	OffsetNumber offset;
 
-		if (buffer == so->curbuf && XLByteEQ(so->stack->lsn, PageGetLSN(p)))
-		{
-			/* page unchanged, so all is simple */
-			offset = ItemPointerGetOffsetNumber(iptr);
-			ItemIdMarkDead(PageGetItemId(p, offset));
-			SetBufferCommitInfoNeedsSave(buffer);
-			LockBuffer(buffer, GIST_UNLOCK);
-			break;
-		}
+	LockBuffer(so->curbuf, GIST_SHARE);
+	gistcheckpage(r, so->curbuf);
+	p = (Page) BufferGetPage(so->curbuf);
 
-		maxoff = PageGetMaxOffsetNumber(p);
+	if (XLByteEQ(so->stack->lsn, PageGetLSN(p)))
+	{
+		/* page unchanged, so all is simple */
+		offset = ItemPointerGetOffsetNumber(iptr);
+		ItemIdMarkDead(PageGetItemId(p, offset));
+		SetBufferCommitInfoNeedsSave(so->curbuf);
+	}
+	else
+	{
+		OffsetNumber maxoff = PageGetMaxOffsetNumber(p);
 
 		for (offset = FirstOffsetNumber; offset <= maxoff; offset = OffsetNumberNext(offset))
 		{
-			IndexTuple	ituple = (IndexTuple) PageGetItem(p, PageGetItemId(p, offset));
+				IndexTuple	ituple = (IndexTuple) PageGetItem(p, PageGetItemId(p, offset));
 
 			if (ItemPointerEquals(&(ituple->t_tid), iptr))
 			{
 				/* found */
 				ItemIdMarkDead(PageGetItemId(p, offset));
-				SetBufferCommitInfoNeedsSave(buffer);
-				LockBuffer(buffer, GIST_UNLOCK);
-				if (buffer != so->curbuf)
-					ReleaseBuffer(buffer);
-				return;
+				SetBufferCommitInfoNeedsSave(so->curbuf);
+				break;
 			}
 		}
-
-		/* follow right link */
-
-		/*
-		 * ??? is it good? if tuple dropped by concurrent vacuum, we will read
-		 * all leaf pages...
-		 */
-		blkno = GistPageGetOpaque(p)->rightlink;
-		LockBuffer(buffer, GIST_UNLOCK);
-		if (buffer != so->curbuf)
-			ReleaseBuffer(buffer);
-
-		if (blkno == InvalidBlockNumber)
-			/* can't found, dropped by somebody else */
-			return;
-		buffer = ReadBuffer(r, blkno);
 	}
+
+	LockBuffer(so->curbuf, GIST_UNLOCK);
 }
 
 /*
@@ -154,7 +130,6 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 	GISTSearchStack *stk;
 	IndexTuple	it;
 	GISTPageOpaque opaque;
-	bool		resetoffset = false;
 	int64		ntids = 0;
 
 	so = (GISTScanOpaque) scan->opaque;
@@ -179,6 +154,50 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 		return 0;
 	}
 
+	/*
+	 * check stored pointers from last visit 
+	 */
+	if ( so->nPageData > 0 ) 
+	{
+		/*
+		 * gistgetmulti never should go here
+		 */
+		Assert( tbm == NULL );
+
+		if ( so->curPageData < so->nPageData )
+		{
+			/*
+			 * pageData is already ordered for scan's direction
+			 */
+			scan->xs_ctup.t_self = so->pageData[ so->curPageData ].iptr;
+			scan->xs_recheck = so->pageData[ so->curPageData ].recheck;
+			so->curPageData ++;
+
+			return 1;
+		}
+		else
+		{
+			/*
+			 * Go to the next page
+			 */
+			stk = so->stack->next;
+			pfree(so->stack);
+			so->stack = stk;
+
+			/* If we're out of stack entries, we're done */
+			if (so->stack == NULL)
+			{
+				ReleaseBuffer(so->curbuf);
+				so->curbuf = InvalidBuffer;
+				return 0;
+			}
+
+			so->curbuf = ReleaseAndReadBuffer(so->curbuf,
+											  scan->indexRelation,
+											  stk->block);
+		}
+	}
+
 	for (;;)
 	{
 		CHECK_FOR_INTERRUPTS();
@@ -189,30 +208,25 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 		gistcheckpage(scan->indexRelation, so->curbuf);
 		p = BufferGetPage(so->curbuf);
 		opaque = GistPageGetOpaque(p);
-		resetoffset = false;
 
-		if (XLogRecPtrIsInvalid(so->stack->lsn) || !XLByteEQ(so->stack->lsn, PageGetLSN(p)))
-		{
-			/* first visit or page changed from last visit, reset offset */
-			so->stack->lsn = PageGetLSN(p);
-			resetoffset = true;
-
-			/* check page split, occured from last visit or visit to parent */
-			if (!XLogRecPtrIsInvalid(so->stack->parentlsn) &&
-				XLByteLT(so->stack->parentlsn, opaque->nsn) &&
-				opaque->rightlink != InvalidBlockNumber /* sanity check */ &&
-				(so->stack->next == NULL || so->stack->next->block != opaque->rightlink)		/* check if already
-					added */ )
-			{
-				/* detect page split, follow right link to add pages */
+		/* remember lsn to identify page changed for tuple's killing */
+		so->stack->lsn = PageGetLSN(p);
 
-				stk = (GISTSearchStack *) palloc(sizeof(GISTSearchStack));
-				stk->next = so->stack->next;
-				stk->block = opaque->rightlink;
-				stk->parentlsn = so->stack->parentlsn;
-				memset(&(stk->lsn), 0, sizeof(GistNSN));
-				so->stack->next = stk;
-			}
+		/* check page split, occured since visit to parent */
+		if (!XLogRecPtrIsInvalid(so->stack->parentlsn) &&
+			XLByteLT(so->stack->parentlsn, opaque->nsn) &&
+			opaque->rightlink != InvalidBlockNumber /* sanity check */ &&
+			(so->stack->next == NULL || so->stack->next->block != opaque->rightlink)		/* check if already
+				added */ )
+		{
+			/* detect page split, follow right link to add pages */
+
+			stk = (GISTSearchStack *) palloc(sizeof(GISTSearchStack));
+			stk->next = so->stack->next;
+			stk->block = opaque->rightlink;
+			stk->parentlsn = so->stack->parentlsn;
+			memset(&(stk->lsn), 0, sizeof(GistNSN));
+			so->stack->next = stk;
 		}
 
 		/* if page is empty, then just skip it */
@@ -235,25 +249,13 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 			continue;
 		}
 
-		if (!GistPageIsLeaf(p) || resetoffset ||
-			!ItemPointerIsValid(&so->curpos))
-		{
-			if (ScanDirectionIsBackward(dir))
-				n = PageGetMaxOffsetNumber(p);
-			else
-				n = FirstOffsetNumber;
-		}
+		if (ScanDirectionIsBackward(dir))
+			n = PageGetMaxOffsetNumber(p);
 		else
-		{
-			n = ItemPointerGetOffsetNumber(&(so->curpos));
-
-			if (ScanDirectionIsBackward(dir))
-				n = OffsetNumberPrev(n);
-			else
-				n = OffsetNumberNext(n);
-		}
+			n = FirstOffsetNumber;
 
 		/* wonderful, we can look at page */
+		so->nPageData = so->curPageData = 0;
 
 		for (;;)
 		{
@@ -261,6 +263,18 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 
 			if (!OffsetNumberIsValid(n))
 			{
+				/*
+				 * If we was called from gistgettuple and current buffer contains
+				 * something matched then make a recursive call - it will return
+				 * ItemPointer from so->pageData. But we save buffer pinned to 
+				 * support tuple's killing
+				 */
+				if ( !tbm && so->nPageData > 0 )
+				{
+					LockBuffer(so->curbuf, GIST_UNLOCK);
+					return gistnext(scan, dir, NULL);
+				}
+
 				/*
 				 * We ran out of matching index entries on the current page,
 				 * so pop the top stack entry and use it to continue the
@@ -306,11 +320,9 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 						tbm_add_tuples(tbm, &it->t_tid, 1, scan->xs_recheck);
 					else 
 					{
-						scan->xs_ctup.t_self = it->t_tid;
-						/* scan->xs_recheck is already set */
-
-						LockBuffer(so->curbuf, GIST_UNLOCK);
-						return ntids; /* always 1 */
+						so->pageData[ so->nPageData ].iptr = it->t_tid;
+						so->pageData[ so->nPageData ].recheck = scan->xs_recheck;
+						so->nPageData ++;
 					}
 				}
 			}

src/backend/access/gist/gistscan.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/gist/gistscan.c,v 1.70 2008/06/19 00:46:03 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gistscan.c,v 1.71 2008/08/23 10:37:24 teodor Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -63,6 +63,7 @@ gistrescan(PG_FUNCTION_ARGS)
 			ReleaseBuffer(so->markbuf);
 			so->markbuf = InvalidBuffer;
 		}
+
 	}
 	else
 	{
@@ -83,6 +84,7 @@ gistrescan(PG_FUNCTION_ARGS)
 	 */
 	ItemPointerSetInvalid(&so->curpos);
 	ItemPointerSetInvalid(&so->markpos);
+	so->nPageData = so->curPageData = 0;
 
 	/* Update scan key, if a new one is given */
 	if (key && scan->numberOfKeys > 0)
@@ -150,6 +152,11 @@ gistmarkpos(PG_FUNCTION_ARGS)
 		so->markbuf = so->curbuf;
 	}
 
+	so->markNPageData = so->nPageData;
+	so->markCurPageData = so->curPageData;
+	if ( so->markNPageData > 0 )
+		memcpy( so->markPageData, so->pageData, sizeof(ItemResult) * so->markNPageData );		
+
 	PG_RETURN_VOID();
 }
 
@@ -199,6 +206,11 @@ gistrestrpos(PG_FUNCTION_ARGS)
 		so->curbuf = so->markbuf;
 	}
 
+	so->nPageData = so->markNPageData;
+	so->curPageData = so->markNPageData;
+	if ( so->markNPageData > 0 )
+		memcpy( so->pageData, so->markPageData, sizeof(ItemResult) * so->markNPageData );		
+
 	PG_RETURN_VOID();
 }
 

src/include/access/gist_private.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/gist_private.h,v 1.31 2008/06/19 00:46:05 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/access/gist_private.h,v 1.32 2008/08/23 10:37:24 teodor Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -58,6 +58,12 @@ typedef struct GISTSTATE
 	TupleDesc	tupdesc;
 } GISTSTATE;
 
+typedef struct ItemResult
+{
+	ItemPointerData		iptr;
+	bool				recheck;
+} ItemResult;
+
 /*
  *	When we're doing a scan, we need to keep track of the parent stack
  *	for the marked and current items.
@@ -73,6 +79,13 @@ typedef struct GISTScanOpaqueData
 	ItemPointerData curpos;
 	Buffer		markbuf;
 	ItemPointerData markpos;
+
+	ItemResult		pageData[BLCKSZ/sizeof(IndexTupleData)];
+	OffsetNumber	nPageData;
+	OffsetNumber	curPageData;
+	ItemResult		markPageData[BLCKSZ/sizeof(IndexTupleData)];
+	OffsetNumber	markNPageData;
+	OffsetNumber	markCurPageData;
 } GISTScanOpaqueData;
 
 typedef GISTScanOpaqueData *GISTScanOpaque;