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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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4
src/backend/access/heap/pruneheap.c
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@ -962,6 +962,10 @@ heap_get_root_tuples(Page page, OffsetNumber *root_offsets)
*/
for (;;)
{
/* Sanity check */
if (nextoffnum < FirstOffsetNumber || nextoffnum > maxoff)
break;
lp = PageGetItemId(page, nextoffnum);
/* Check for broken chains */