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visibilitymap.c about when rd_fsm_nblocks and rd_vm_nblocks can be out of
date.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, 12 insertions, 1 deletions

diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h
index 3cf02776311..d7e267729d3 100644
--- a/src/include/storage/smgr.h
+++ b/src/include/storage/smgr.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/smgr.h,v 1.69 2010/01/02 16:58:08 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/smgr.h,v 1.70 2010/02/09 21:43:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -43,6 +43,17 @@ typedef struct SMgrRelationData
 	/* pointer to owning pointer, or NULL if none */
 	struct SMgrRelationData **smgr_owner;
 
+	/*
+	 * These next three fields are not actually used or manipulated by smgr,
+	 * except that they are reset to InvalidBlockNumber upon a cache flush
+	 * event (in particular, upon truncation of the relation).  Higher levels
+	 * store cached state here so that it will be reset when truncation
+	 * happens.  In all three cases, InvalidBlockNumber means "unknown".
+	 */
+	BlockNumber smgr_targblock;		/* current insertion target block */
+	BlockNumber smgr_fsm_nblocks;	/* last known size of fsm fork */
+	BlockNumber smgr_vm_nblocks;	/* last known size of vm fork */
+
 	/* additional public fields may someday exist here */
 
 	/*