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 6359c2753154ddbb5931f457ee4f101dd2f60f64..8011567f66a3e04d228b5818b6f8f62c2b47cbfe 100644 (file)
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.262 2003/09/29 00:05:25 petere Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.263 2003/10/02 23:19:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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);