Dept of second thoughts: after studying index_getnext() a bit more I realize

tglsfdc · tglsfdc · commit 7d535ebe5bf9 · 2009-11-01T22:30:54.000Z
that it can scribble on scan-&gt;xs_ctup.t_self while following HOT chains,
so we can't rely on that to stay valid between hashgettuple() calls.
Introduce a private variable in HashScanOpaque, instead.
diff --git a/src/backend/access/hash/hash.c b/src/backend/access/hash/hash.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.114 2009/11/01 21:25:25 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.115 2009/11/01 22:30:54 tgl Exp $
  *
  * NOTES
  *	  This file contains only the public interface routines.
@@ -251,7 +251,7 @@ hashgettuple(PG_FUNCTION_ARGS)
 			IndexTuple	itup;
 
 			itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offnum));
-			if (ItemPointerEquals(&scan->xs_ctup.t_self, &itup->t_tid))
+			if (ItemPointerEquals(&(so->hashso_heappos), &(itup->t_tid)))
 				break;
 		}
 		if (offnum > maxoffnum)
@@ -304,6 +304,9 @@ hashgettuple(PG_FUNCTION_ARGS)
 	if (BufferIsValid(so->hashso_curbuf))
 		_hash_chgbufaccess(rel, so->hashso_curbuf, HASH_READ, HASH_NOLOCK);
 
+	/* Return current heap TID on success */
+	scan->xs_ctup.t_self = so->hashso_heappos;
+
 	PG_RETURN_BOOL(res);
 }
 
@@ -345,7 +348,7 @@ hashgetbitmap(PG_FUNCTION_ARGS)
 		if (add_tuple)
 		{
 			/* Note we mark the tuple ID as requiring recheck */
-			tbm_add_tuples(tbm, &scan->xs_ctup.t_self, 1, true);
+			tbm_add_tuples(tbm, &(so->hashso_heappos), 1, true);
 			ntids++;
 		}
 
@@ -375,6 +378,7 @@ hashbeginscan(PG_FUNCTION_ARGS)
 	so->hashso_curbuf = InvalidBuffer;
 	/* set position invalid (this will cause _hash_first call) */
 	ItemPointerSetInvalid(&(so->hashso_curpos));
+	ItemPointerSetInvalid(&(so->hashso_heappos));
 
 	scan->opaque = so;
 
@@ -410,6 +414,7 @@ hashrescan(PG_FUNCTION_ARGS)
 
 		/* set position invalid (this will cause _hash_first call) */
 		ItemPointerSetInvalid(&(so->hashso_curpos));
+		ItemPointerSetInvalid(&(so->hashso_heappos));
 	}
 
 	/* Update scan key, if a new one is given */
diff --git a/src/backend/access/hash/hashsearch.c b/src/backend/access/hash/hashsearch.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/hash/hashsearch.c,v 1.57 2009/06/11 14:48:53 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/hash/hashsearch.c,v 1.58 2009/11/01 22:30:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -58,7 +58,7 @@ _hash_next(IndexScanDesc scan, ScanDirection dir)
 	_hash_checkpage(rel, buf, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
 	page = BufferGetPage(buf);
 	itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offnum));
-	scan->xs_ctup.t_self = itup->t_tid;
+	so->hashso_heappos = itup->t_tid;
 
 	return true;
 }
@@ -242,7 +242,7 @@ _hash_first(IndexScanDesc scan, ScanDirection dir)
 	_hash_checkpage(rel, buf, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
 	page = BufferGetPage(buf);
 	itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offnum));
-	scan->xs_ctup.t_self = itup->t_tid;
+	so->hashso_heappos = itup->t_tid;
 
 	return true;
 }
diff --git a/src/include/access/hash.h b/src/include/access/hash.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/hash.h,v 1.94 2009/11/01 21:25:25 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/hash.h,v 1.95 2009/11/01 22:30:54 tgl Exp $
  *
  * NOTES
  *		modeled after Margo Seltzer's hash implementation for unix.
@@ -99,8 +99,11 @@ typedef struct HashScanOpaqueData
 	 */
 	Buffer		hashso_curbuf;
 
-	/* Current position of the scan */
+	/* Current position of the scan, as an index TID */
 	ItemPointerData hashso_curpos;
+
+	/* Current position of the scan, as a heap TID */
+	ItemPointerData hashso_heappos;
 } HashScanOpaqueData;
 
 typedef HashScanOpaqueData *HashScanOpaque;

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.114 2009/11/01 21:25:25 tgl Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.115 2009/11/01 22:30:54 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`* NOTES`
`14`	`14`	`* This file contains only the public interface routines.`
`@@ -251,7 +251,7 @@ hashgettuple(PG_FUNCTION_ARGS)`
`251`	`251`	`IndexTuple itup;`
`252`	`252`
`253`	`253`	`itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offnum));`
`254`		`- if (ItemPointerEquals(&scan->xs_ctup.t_self, &itup->t_tid))`
	`254`	`+ if (ItemPointerEquals(&(so->hashso_heappos), &(itup->t_tid)))`
`255`	`255`	`break;`
`256`	`256`	`}`
`257`	`257`	`if (offnum > maxoffnum)`
`@@ -304,6 +304,9 @@ hashgettuple(PG_FUNCTION_ARGS)`
`304`	`304`	`if (BufferIsValid(so->hashso_curbuf))`
`305`	`305`	`_hash_chgbufaccess(rel, so->hashso_curbuf, HASH_READ, HASH_NOLOCK);`
`306`	`306`
	`307`	`+ /* Return current heap TID on success */`
	`308`	`+ scan->xs_ctup.t_self = so->hashso_heappos;`
	`309`	`+`
`307`	`310`	`PG_RETURN_BOOL(res);`
`308`	`311`	`}`
`309`	`312`
`@@ -345,7 +348,7 @@ hashgetbitmap(PG_FUNCTION_ARGS)`
`345`	`348`	`if (add_tuple)`
`346`	`349`	`{`
`347`	`350`	`/* Note we mark the tuple ID as requiring recheck */`
`348`		`- tbm_add_tuples(tbm, &scan->xs_ctup.t_self, 1, true);`
	`351`	`+ tbm_add_tuples(tbm, &(so->hashso_heappos), 1, true);`
`349`	`352`	`ntids++;`
`350`	`353`	`}`
`351`	`354`
`@@ -375,6 +378,7 @@ hashbeginscan(PG_FUNCTION_ARGS)`
`375`	`378`	`so->hashso_curbuf = InvalidBuffer;`
`376`	`379`	`/* set position invalid (this will cause _hash_first call) */`
`377`	`380`	`ItemPointerSetInvalid(&(so->hashso_curpos));`
	`381`	`+ ItemPointerSetInvalid(&(so->hashso_heappos));`
`378`	`382`
`379`	`383`	`scan->opaque = so;`
`380`	`384`
`@@ -410,6 +414,7 @@ hashrescan(PG_FUNCTION_ARGS)`
`410`	`414`
`411`	`415`	`/* set position invalid (this will cause _hash_first call) */`
`412`	`416`	`ItemPointerSetInvalid(&(so->hashso_curpos));`
	`417`	`+ ItemPointerSetInvalid(&(so->hashso_heappos));`
`413`	`418`	`}`
`414`	`419`
`415`	`420`	`/* Update scan key, if a new one is given */`