Fix up rickety handling of relation-truncation interlocks.

Move rd_targblock, rd_fsm_nblocks, and rd_vm_nblocks from relcache to the smgr
relation entries, so that they will get reset to InvalidBlockNumber whenever
an smgr-level flush happens.  Because we now send smgr invalidation messages
immediately (not at end of transaction) when a relation truncation occurs,
this ensures that other backends will reset their values before they next
access the relation.  We no longer need the unreliable assumption that a
VACUUM that's doing a truncation will hold its AccessExclusive lock until
commit --- in fact, we can intentionally release that lock as soon as we've
completed the truncation.  This patch therefore reverts (most of) Alvaro's
patch of 2009-11-10, as well as my marginal hacking on it yesterday.  We can
also get rid of assorted no-longer-needed relcache flushes, which are far more
expensive than an smgr flush because they kill a lot more state.

In passing this patch fixes smgr_redo's failure to perform visibility-map
truncation, and cleans up some rather dubious assumptions in freespace.c and
visibilitymap.c about when rd_fsm_nblocks and rd_vm_nblocks can be out of
date.

1 files changed, 46 insertions, 32 deletions

diff --git a/src/backend/access/heap/visibilitymap.c b/src/backend/access/heap/visibilitymap.c
index d89ef06d344..dbfb3df2d0d 100644
--- a/src/backend/access/heap/visibilitymap.c
+++ b/src/backend/access/heap/visibilitymap.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/visibilitymap.c,v 1.7 2010/01/02 16:57:35 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/visibilitymap.c,v 1.8 2010/02/09 21:43:29 tgl Exp $
  *
  * INTERFACE ROUTINES
  *		visibilitymap_clear - clear a bit in the visibility map
@@ -94,7 +94,7 @@
 #include "storage/bufpage.h"
 #include "storage/lmgr.h"
 #include "storage/smgr.h"
-#include "utils/inval.h"
+
 
 /*#define TRACE_VISIBILITYMAP */
 
@@ -291,7 +291,13 @@ visibilitymap_test(Relation rel, BlockNumber heapBlk, Buffer *buf)
 }
 
 /*
- *	visibilitymap_test - truncate the visibility map
+ *	visibilitymap_truncate - truncate the visibility map
+ *
+ * The caller must hold AccessExclusiveLock on the relation, to ensure that
+ * other backends receive the smgr invalidation event that this function sends
+ * before they access the VM again.
+ *
+ * nheapblocks is the new size of the heap.
  */
 void
 visibilitymap_truncate(Relation rel, BlockNumber nheapblocks)
@@ -307,6 +313,8 @@ visibilitymap_truncate(Relation rel, BlockNumber nheapblocks)
 	elog(DEBUG1, "vm_truncate %s %d", RelationGetRelationName(rel), nheapblocks);
 #endif
 
+	RelationOpenSmgr(rel);
+
 	/*
 	 * If no visibility map has been created yet for this relation, there's
 	 * nothing to truncate.
@@ -358,23 +366,25 @@ visibilitymap_truncate(Relation rel, BlockNumber nheapblocks)
 	else
 		newnblocks = truncBlock;
 
-	if (smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM) < newnblocks)
+	if (smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM) <= newnblocks)
 	{
 		/* nothing to do, the file was already smaller than requested size */
 		return;
 	}
 
+	/* Truncate the unused VM pages, and send smgr inval message */
 	smgrtruncate(rel->rd_smgr, VISIBILITYMAP_FORKNUM, newnblocks,
 				 rel->rd_istemp);
 
 	/*
-	 * Need to invalidate the relcache entry, because rd_vm_nblocks seen by
-	 * other backends is no longer valid.
+	 * We might as well update the local smgr_vm_nblocks setting.
+	 * smgrtruncate sent an smgr cache inval message, which will cause
+	 * other backends to invalidate their copy of smgr_vm_nblocks, and
+	 * this one too at the next command boundary.  But this ensures it
+	 * isn't outright wrong until then.
 	 */
-	if (!InRecovery)
-		CacheInvalidateRelcache(rel);
-
-	rel->rd_vm_nblocks = newnblocks;
+	if (rel->rd_smgr)
+		rel->rd_smgr->smgr_vm_nblocks = newnblocks;
 }
 
 /*
@@ -391,21 +401,23 @@ vm_readbuf(Relation rel, BlockNumber blkno, bool extend)
 	RelationOpenSmgr(rel);
 
 	/*
-	 * The current size of the visibility map fork is kept in relcache, to
-	 * avoid reading beyond EOF. If we haven't cached the size of the map yet,
-	 * do that first.
+	 * If we haven't cached the size of the visibility map fork yet, check it
+	 * first.  Also recheck if the requested block seems to be past end, since
+	 * our cached value might be stale.  (We send smgr inval messages on
+	 * truncation, but not on extension.)
 	 */
-	if (rel->rd_vm_nblocks == InvalidBlockNumber)
+	if (rel->rd_smgr->smgr_vm_nblocks == InvalidBlockNumber ||
+		blkno >= rel->rd_smgr->smgr_vm_nblocks)
 	{
 		if (smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
-			rel->rd_vm_nblocks = smgrnblocks(rel->rd_smgr,
-											 VISIBILITYMAP_FORKNUM);
+			rel->rd_smgr->smgr_vm_nblocks = smgrnblocks(rel->rd_smgr,
+														VISIBILITYMAP_FORKNUM);
 		else
-			rel->rd_vm_nblocks = 0;
+			rel->rd_smgr->smgr_vm_nblocks = 0;
 	}
 
 	/* Handle requests beyond EOF */
-	if (blkno >= rel->rd_vm_nblocks)
+	if (blkno >= rel->rd_smgr->smgr_vm_nblocks)
 	{
 		if (extend)
 			vm_extend(rel, blkno + 1);
@@ -446,19 +458,23 @@ vm_extend(Relation rel, BlockNumber vm_nblocks)
 	 * separate lock tag type for it.
 	 *
 	 * Note that another backend might have extended or created the relation
-	 * before we get the lock.
+	 * by the time we get the lock.
 	 */
 	LockRelationForExtension(rel, ExclusiveLock);
 
-	/* Create the file first if it doesn't exist */
-	if ((rel->rd_vm_nblocks == 0 || rel->rd_vm_nblocks == InvalidBlockNumber)
-		&& !smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
-	{
+	/* Might have to re-open if a cache flush happened */
+	RelationOpenSmgr(rel);
+
+	/*
+	 * Create the file first if it doesn't exist.  If smgr_vm_nblocks
+	 * is positive then it must exist, no need for an smgrexists call.
+	 */
+	if ((rel->rd_smgr->smgr_vm_nblocks == 0 ||
+		 rel->rd_smgr->smgr_vm_nblocks == InvalidBlockNumber) &&
+		!smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
 		smgrcreate(rel->rd_smgr, VISIBILITYMAP_FORKNUM, false);
-		vm_nblocks_now = 0;
-	}
-	else
-		vm_nblocks_now = smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM);
+
+	vm_nblocks_now = smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM);
 
 	while (vm_nblocks_now < vm_nblocks)
 	{
@@ -467,12 +483,10 @@ vm_extend(Relation rel, BlockNumber vm_nblocks)
 		vm_nblocks_now++;
 	}
 
+	/* Update local cache with the up-to-date size */
+	rel->rd_smgr->smgr_vm_nblocks = vm_nblocks_now;
+
 	UnlockRelationForExtension(rel, ExclusiveLock);
 
 	pfree(pg);
-
-	/* Update the relcache with the up-to-date size */
-	if (!InRecovery)
-		CacheInvalidateRelcache(rel);
-	rel->rd_vm_nblocks = vm_nblocks_now;
 }