From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 2 Oct 2003 23:19:44 +0000 (+0000)
Subject: Add a bit more locking to vac_update_relstats and vac_update_dbstats
X-Git-Url: http://waps.l3s.uni-hannover.de/gitweb/?a=commitdiff_plain;h=c370c7715abf79add510a3245f995dca447ce09a;p=users%2Fbernd%2Fpostgres.git

Add a bit more locking to vac_update_relstats and vac_update_dbstats
to make them comparable to what UpdateStats does in the same situation.
I'm not certain two instances of vac_update_relstats could run in
parallel for the same relation, but parallel invocations of vac_update_dbstats
do seem possible.
---

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 8e40932a54..146f28272b 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -520,6 +520,9 @@ vac_update_relstats(Oid relid, BlockNumber num_pages, double num_tuples,
 		elog(ERROR, "pg_class entry for relid %u vanished during vacuuming",
 			 relid);
 
+	/* ensure no one else does this at the same time */
+	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
 	/* overwrite the existing statistics in the tuple */
 	pgcform = (Form_pg_class) GETSTRUCT(&rtup);
 	pgcform->relpages = (int32) num_pages;
@@ -533,6 +536,8 @@ vac_update_relstats(Oid relid, BlockNumber num_pages, double num_tuples,
 	if (!hasindex)
 		pgcform->relhaspkey = false;
 
+	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+
 	/*
 	 * Invalidate the tuple in the catcaches; this also arranges to flush
 	 * the relation's relcache entry.  (If we fail to commit for some
@@ -588,12 +593,17 @@ vac_update_dbstats(Oid dbid,
 	if (!HeapTupleIsValid(tuple))
 		elog(ERROR, "could not find tuple for database %u", dbid);
 
+	/* ensure no one else does this at the same time */
+	LockBuffer(scan->rs_cbuf, BUFFER_LOCK_EXCLUSIVE);
+
 	dbform = (Form_pg_database) GETSTRUCT(tuple);
 
 	/* overwrite the existing statistics in the tuple */
 	dbform->datvacuumxid = vacuumXID;
 	dbform->datfrozenxid = frozenXID;
 
+	LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
+
 	/* invalidate the tuple in the cache and write the buffer */
 	CacheInvalidateHeapTuple(relation, tuple);
 	WriteNoReleaseBuffer(scan->rs_cbuf);