Fix vac_update_relstats to ensure it always sends a relcache inval message,

tglsfdc · tglsfdc · commit 2825337232af · 2007-03-08T17:03:31.000Z
even if none of the fields in the pg_class row change.  This behavior is
necessary to ensure other backends flush rd_targblock values that might
point to truncated-away pages.  We got this right pre-8.2 but it was broken
by overoptimistic change to not write out the pg_class row if unchanged.
Per report from Pavan Deolasee.
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.346 2007/02/15 23:23:22 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.347 2007/03/08 17:03:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -715,10 +715,20 @@ vac_update_relstats(Oid relid, BlockNumber num_pages, double num_tuples,
 	}
 
 	/*
-	 * If anything changed, write out the tuple
+	 * If anything changed, write out the tuple.  Even if nothing changed,
+	 * force relcache invalidation so all backends reset their rd_targblock
+	 * --- otherwise it might point to a page we truncated away.
 	 */
 	if (dirty)
+	{
 		heap_inplace_update(rd, ctup);
+		/* the above sends a cache inval message */
+	}
+	else
+	{
+		/* no need to change tuple, but force relcache inval anyway */
+		CacheInvalidateRelcacheByTuple(ctup);
+	}
 
 	heap_close(rd, RowExclusiveLock);
 }

Original file line number	Diff line number	Diff line change
`@@ -13,7 +13,7 @@`
`13`	`13`	`*`
`14`	`14`	`*`
`15`	`15`	`* IDENTIFICATION`
`16`		`- * $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.346 2007/02/15 23:23:22 alvherre Exp $`
	`16`	`+ * $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.347 2007/03/08 17:03:31 tgl Exp $`
`17`	`17`	`*`
`18`	`18`	`*-------------------------------------------------------------------------`
`19`	`19`	`*/`
`@@ -715,10 +715,20 @@ vac_update_relstats(Oid relid, BlockNumber num_pages, double num_tuples,`
`715`	`715`	`}`
`716`	`716`
`717`	`717`	`/*`
`718`		`- * If anything changed, write out the tuple`
	`718`	`+ * If anything changed, write out the tuple. Even if nothing changed,`
	`719`	`+ * force relcache invalidation so all backends reset their rd_targblock`
	`720`	`+ * --- otherwise it might point to a page we truncated away.`
`719`	`721`	`*/`
`720`	`722`	`if (dirty)`
	`723`	`+ {`
`721`	`724`	`heap_inplace_update(rd, ctup);`
	`725`	`+ /* the above sends a cache inval message */`
	`726`	`+ }`
	`727`	`+ else`
	`728`	`+ {`
	`729`	`+ /* no need to change tuple, but force relcache inval anyway */`
	`730`	`+ CacheInvalidateRelcacheByTuple(ctup);`
	`731`	`+ }`
`722`	`732`
`723`	`733`	`heap_close(rd, RowExclusiveLock);`
`724`	`734`	`}`