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Adjust lazy_scan_heap() accounting comments.

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Explain which particular LP_DEAD line pointers get accounted for by the
tups_vacuumed variable.
This commit is contained in:
Peter Geoghegan
2021-02-14 19:28:37 -08:00
parent f900a79ecd
commit 7cde6b13a9
2 changed files with 12 additions and 11 deletions
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18
src/backend/access/heap/vacuumlazy.c
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@ -765,9 +765,9 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
next_fsm_block_to_vacuum;
double num_tuples, /* total number of nonremovable tuples */
live_tuples, /* live tuples (reltuples estimate) */
tups_vacuumed, /* tuples cleaned up by vacuum */
tups_vacuumed, /* tuples cleaned up by current vacuum */
nkeep, /* dead-but-not-removable tuples */
nunused; /* unused line pointers */
nunused; /* # existing unused line pointers */
IndexBulkDeleteResult **indstats;
int i;
PGRUsage ru0;
@ -1234,7 +1234,8 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
/*
* Prune all HOT-update chains in this page.
*
* We count tuples removed by the pruning step as removed by VACUUM.
* We count tuples removed by the pruning step as removed by VACUUM
* (existing LP_DEAD line pointers don't count).
*/
tups_vacuumed += heap_page_prune(onerel, buf, vistest, false,
InvalidTransactionId, 0,
@ -1286,10 +1287,13 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
ItemPointerSet(&(tuple.t_self), blkno, offnum);
/*
* DEAD line pointers are to be vacuumed normally; but we don't
* LP_DEAD line pointers are to be vacuumed normally; but we don't
* count them in tups_vacuumed, else we'd be double-counting (at
* least in the common case where heap_page_prune() just freed up
* a non-HOT tuple).
* a non-HOT tuple). Note also that the final tups_vacuumed value
* might be very low for tables where opportunistic page pruning
* happens to occur very frequently (via heap_page_prune_opt()
* calls that free up non-HOT tuples).
*/
if (ItemIdIsDead(itemid))
{
@ -1742,10 +1746,6 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
vacrelstats->relname,
tups_vacuumed, vacuumed_pages)));
/*
* This is pretty messy, but we split it up so that we can skip emitting
* individual parts of the message when not applicable.
*/
initStringInfo(&buf);
appendStringInfo(&buf,
_("%.0f dead row versions cannot be removed yet, oldest xmin: %u\n"),