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| author | Peter Geoghegan <pg@bowt.ie> | 2021-02-14 19:28:37 -0800 |
|---|---|---|
| committer | Peter Geoghegan <pg@bowt.ie> | 2021-02-14 19:28:37 -0800 |
| commit | 7cde6b13a9b630e2f04d91e2f17dedc2afee21c6 (patch) | |
| tree | ba66e8f40ff0fd4866cb034888fdca3bbee1c330 /src | |
| parent | f900a79ecdc1864a6ead72c97c34a41012227eaf (diff) | |
| download | postgresql-7cde6b13a9b630e2f04d91e2f17dedc2afee21c6.tar.gz postgresql-7cde6b13a9b630e2f04d91e2f17dedc2afee21c6.zip | |
Adjust lazy_scan_heap() accounting comments.
Explain which particular LP_DEAD line pointers get accounted for by the
tups_vacuumed variable.
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/access/heap/pruneheap.c | 5 | ||||
| -rw-r--r-- | src/backend/access/heap/vacuumlazy.c | 18 |
2 files changed, 12 insertions, 11 deletions
diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c index e3a716a2a2f..8bb38d6406e 100644 --- a/src/backend/access/heap/pruneheap.c +++ b/src/backend/access/heap/pruneheap.c @@ -213,11 +213,12 @@ heap_page_prune_opt(Relation relation, Buffer buffer) * send its own new total to pgstats, and we don't want this delta applied * on top of that.) * + * Sets latestRemovedXid for caller on return. + * * off_loc is the offset location required by the caller to use in error * callback. * - * Returns the number of tuples deleted from the page and sets - * latestRemovedXid. + * Returns the number of tuples deleted from the page during this call. */ int heap_page_prune(Relation relation, Buffer buffer, diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index f3d2265fad7..e9bd6dba80f 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -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"), |