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Truncate line pointer array during VACUUM.

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Teach VACUUM to truncate the line pointer array of each heap page when a
contiguous group of LP_UNUSED line pointers appear at the end of the
array -- these unused and unreferenced items are excluded.  This process
occurs during VACUUM's second pass over the heap, right after LP_DEAD
line pointers on the page (those encountered/pruned during the first
pass) are marked LP_UNUSED.

Truncation avoids line pointer bloat with certain workloads,
particularly those involving continual range DELETEs and bulk INSERTs
against the same table.

Also harden heapam code to check for an out-of-range page offset number
in places where we weren't already doing so.

Author: Matthias van de Meent <boekewurm+postgres@gmail.com>
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-By: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAEze2WjgaQc55Y5f5CQd3L=eS5CZcff2Obxp=O6pto8-f0hC4w@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-Wzn6a64PJM1Ggzm=uvx2otsopJMhFQj_g1rAj4GWr3ZSzw@mail.gmail.com
This commit is contained in:
Peter Geoghegan
2021-04-07 08:47:15 -07:00
parent 3db826bd55
commit 3c3b8a4b26
5 changed files with 144 additions and 11 deletions
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16
src/backend/access/heap/vacuumlazy.c
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@ -1444,7 +1444,11 @@ lazy_scan_heap(LVRelState *vacrel, VacuumParams *params, bool aggressive)
if (prunestate.has_lpdead_items && vacrel->do_index_vacuuming)
{
/*
* Wait until lazy_vacuum_heap_rel() to save free space.
* Wait until lazy_vacuum_heap_rel() to save free space. This
* doesn't just save us some cycles; it also allows us to record
* any additional free space that lazy_vacuum_heap_page() will
* make available in cases where it's possible to truncate the
* page's line pointer array.
*
* Note: The one-pass (no indexes) case is only supposed to make
* it this far when there were no LP_DEAD items during pruning.
@ -2033,6 +2037,13 @@ lazy_vacuum_all_indexes(LVRelState *vacrel)
* Pages that never had lazy_scan_prune record LP_DEAD items are not visited
* at all.
*
* We may also be able to truncate the line pointer array of the heap pages we
* visit. If there is a contiguous group of LP_UNUSED items at the end of the
* array, it can be reclaimed as free space. These LP_UNUSED items usually
* start out as LP_DEAD items recorded by lazy_scan_prune (we set items from
* each page to LP_UNUSED, and then consider if it's possible to truncate the
* page's line pointer array).
*
* Note: the reason for doing this as a second pass is we cannot remove the
* tuples until we've removed their index entries, and we want to process
* index entry removal in batches as large as possible.
@ -2175,7 +2186,8 @@ lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno, Buffer buffer,
Assert(uncnt > 0);
PageSetHasFreeLinePointers(page);
/* Attempt to truncate line pointer array now */
PageTruncateLinePointerArray(page);
/*
* Mark buffer dirty before we write WAL.