Correct heap vacuum boundary state setup ordering

052026c9b9 mistakenly reordered setup steps in heap_vacuum_rel(),
incorrectly moving RelationGetNumberOfBlocks() before
vacuum_get_cutoffs().

OldestXmin must be determined before RelationGetNumberOfBlocks()
calculates the number of blocks in the relation that will be vacuumed.
Otherwise tuples older than OldestXmin may be inserted into the end of
the relation into blocks that are not vacuumed. If additional tuples
newer than those inserted into unscanned blocks but older than
OldestXmin are inserted into free space earlier in the relation, the
result could be advancing pg_class.relfrozenxid to a newer value than an
unfrozen XID in one of the unscanned heap pages.

Assigning an incorrect relfrozenxid can lead to data loss, so it is
imperative that it correctly reflect the oldest unfrozen xid.

Reported-by: Peter Geoghegan <pg@bowt.ie>
Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-WzntqvVEdbbpqG5JqSZGuLWmy4PBfUO-OswfivKchr2gvw%40mail.gmail.com

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 708674d8fcf4a02f9d543a72918229b4a34e7fd0..09416450af96221edb25d6dad9112683561438f7 100644 (file)
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -757,7 +757,6 @@ heap_vacuum_rel(Relation rel, VacuumParams *params,
    vacrel->vm_new_visible_pages = 0;
    vacrel->vm_new_visible_frozen_pages = 0;
    vacrel->vm_new_frozen_pages = 0;
-   vacrel->rel_pages = orig_rel_pages = RelationGetNumberOfBlocks(rel);
 
    /*
     * Get cutoffs that determine which deleted tuples are considered DEAD,
@@ -776,7 +775,9 @@ heap_vacuum_rel(Relation rel, VacuumParams *params,
     * to increase the number of dead tuples it can prune away.)
     */
    vacrel->aggressive = vacuum_get_cutoffs(rel, params, &vacrel->cutoffs);
+   vacrel->rel_pages = orig_rel_pages = RelationGetNumberOfBlocks(rel);
    vacrel->vistest = GlobalVisTestFor(rel);
+
    /* Initialize state used to track oldest extant XID/MXID */
    vacrel->NewRelfrozenXid = vacrel->cutoffs.OldestXmin;
    vacrel->NewRelminMxid = vacrel->cutoffs.OldestMxact;