Revise the TIDBitmap API to support multiple concurrent iterations over a

bitmap.  This is extracted from Greg Stark's posix_fadvise patch; it seems
worth committing separately, since it's potentially useful independently of
posix_fadvise.

Author: tglsfdc

src/backend/access/gin/ginget.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginget.c,v 1.21 2009/01/01 17:23:34 momjian Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginget.c,v 1.22 2009/01/10 21:08:36 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -290,6 +290,7 @@ startScanEntry(Relation index, GinState *ginstate, GinScanEntry entry)
 	entry->list = NULL;
 	entry->nlist = 0;
 	entry->partialMatch = NULL;
+	entry->partialMatchIterator = NULL;
 	entry->partialMatchResult = NULL;
 	entry->reduceResult = FALSE;
 	entry->predictNumberResult = 0;
@@ -311,6 +312,9 @@ startScanEntry(Relation index, GinState *ginstate, GinScanEntry entry)
 			 */
 			if ( entry->partialMatch )
 			{
+				if (entry->partialMatchIterator)
+					tbm_end_iterate(entry->partialMatchIterator);
+				entry->partialMatchIterator = NULL;
 				tbm_free( entry->partialMatch );
 				entry->partialMatch = NULL;
 			}
@@ -323,7 +327,7 @@ startScanEntry(Relation index, GinState *ginstate, GinScanEntry entry)
 
 		if ( entry->partialMatch && !tbm_is_empty(entry->partialMatch) )
 		{
-			tbm_begin_iterate(entry->partialMatch);
+			entry->partialMatchIterator = tbm_begin_iterate(entry->partialMatch);
 			entry->isFinished = FALSE;
 		}
 	}
@@ -534,11 +538,13 @@ entryGetItem(Relation index, GinScanEntry entry)
 		{
 			if ( entry->partialMatchResult == NULL || entry->offset >= entry->partialMatchResult->ntuples )
 			{
-				entry->partialMatchResult = tbm_iterate( entry->partialMatch );
+				entry->partialMatchResult = tbm_iterate( entry->partialMatchIterator );
 
 				if ( entry->partialMatchResult == NULL )
 				{
 					ItemPointerSet(&entry->curItem, InvalidBlockNumber, InvalidOffsetNumber);
+					tbm_end_iterate(entry->partialMatchIterator);
+					entry->partialMatchIterator = NULL;
 					entry->isFinished = TRUE;
 					break;
 				}

src/backend/access/gin/ginscan.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginscan.c,v 1.20 2009/01/01 17:23:34 momjian Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginscan.c,v 1.21 2009/01/10 21:08:36 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -61,6 +61,8 @@ fillScanKey(GinState *ginstate, GinScanKey key, OffsetNumber attnum, Datum query
 		key->scanEntry[i].offset = InvalidOffsetNumber;
 		key->scanEntry[i].buffer = InvalidBuffer;
 		key->scanEntry[i].partialMatch = NULL;
+		key->scanEntry[i].partialMatchIterator = NULL;
+		key->scanEntry[i].partialMatchResult = NULL;
 		key->scanEntry[i].strategy = strategy;
 		key->scanEntry[i].list = NULL;
 		key->scanEntry[i].nlist = 0;
@@ -107,6 +109,7 @@ resetScanKeys(GinScanKey keys, uint32 nkeys)
 			key->scanEntry[j].list = NULL;
 			key->scanEntry[j].nlist = 0;
 			key->scanEntry[j].partialMatch = NULL;
+			key->scanEntry[j].partialMatchIterator = NULL;
 			key->scanEntry[j].partialMatchResult = NULL;
 		}
 	}
@@ -132,6 +135,8 @@ freeScanKeys(GinScanKey keys, uint32 nkeys)
 				ReleaseBuffer(key->scanEntry[j].buffer);
 			if (key->scanEntry[j].list)
 				pfree(key->scanEntry[j].list);
+			if (key->scanEntry[j].partialMatchIterator)
+				tbm_end_iterate(key->scanEntry[j].partialMatchIterator);
 			if (key->scanEntry[j].partialMatch)
 				tbm_free(key->scanEntry[j].partialMatch);
 		}

src/backend/executor/nodeBitmapHeapscan.c

@@ -21,7 +21,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.31 2009/01/01 17:23:41 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.32 2009/01/10 21:08:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -65,6 +65,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 	HeapScanDesc scan;
 	Index		scanrelid;
 	TIDBitmap  *tbm;
+	TBMIterator *tbmiterator;
 	TBMIterateResult *tbmres;
 	OffsetNumber targoffset;
 	TupleTableSlot *slot;
@@ -78,6 +79,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 	scan = node->ss.ss_currentScanDesc;
 	scanrelid = ((BitmapHeapScan *) node->ss.ps.plan)->scan.scanrelid;
 	tbm = node->tbm;
+	tbmiterator = node->tbmiterator;
 	tbmres = node->tbmres;
 
 	/*
@@ -111,7 +113,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 
 	/*
 	 * If we haven't yet performed the underlying index scan, do it, and
-	 * prepare the bitmap to be iterated over.
+	 * begin the iteration over the bitmap.
 	 */
 	if (tbm == NULL)
 	{
@@ -121,9 +123,8 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			elog(ERROR, "unrecognized result from subplan");
 
 		node->tbm = tbm;
+		node->tbmiterator = tbmiterator = tbm_begin_iterate(tbm);
 		node->tbmres = tbmres = NULL;
-
-		tbm_begin_iterate(tbm);
 	}
 
 	for (;;)
@@ -136,7 +137,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 		 */
 		if (tbmres == NULL)
 		{
-			node->tbmres = tbmres = tbm_iterate(tbm);
+			node->tbmres = tbmres = tbm_iterate(tbmiterator);
 			if (tbmres == NULL)
 			{
 				/* no more entries in the bitmap */
@@ -376,9 +377,12 @@ ExecBitmapHeapReScan(BitmapHeapScanState *node, ExprContext *exprCtxt)
 	/* rescan to release any page pin */
 	heap_rescan(node->ss.ss_currentScanDesc, NULL);
 
+	if (node->tbmiterator)
+		tbm_end_iterate(node->tbmiterator);
 	if (node->tbm)
 		tbm_free(node->tbm);
 	node->tbm = NULL;
+	node->tbmiterator = NULL;
 	node->tbmres = NULL;
 
 	/*
@@ -423,6 +427,8 @@ ExecEndBitmapHeapScan(BitmapHeapScanState *node)
 	/*
 	 * release bitmap if any
 	 */
+	if (node->tbmiterator)
+		tbm_end_iterate(node->tbmiterator);
 	if (node->tbm)
 		tbm_free(node->tbm);
 
@@ -466,6 +472,7 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
 	scanstate->ss.ps.state = estate;
 
 	scanstate->tbm = NULL;
+	scanstate->tbmiterator = NULL;
 	scanstate->tbmres = NULL;
 
 	/*