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 8e40932a54ae40f4613f3f776de33e68e55f1e8c..146f28272b92aeafea4c34923ac33860b2cb6d86 100644 (file)
--- 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);