database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-10-22 14:32:25 +03:00
Code Activity

Add options to control whether VACUUM runs vac_update_datfrozenxid.

Browse Source 
VACUUM normally ends by running vac_update_datfrozenxid(), which
requires a scan of pg_class.  Therefore, if one attempts to vacuum a
database one table at a time --- as vacuumdb has done since v12 ---
we will spend O(N^2) time in vac_update_datfrozenxid().  That causes
serious performance problems in databases with tens of thousands of
tables, and indeed the effect is measurable with only a few hundred.
To add insult to injury, only one process can run
vac_update_datfrozenxid at the same time per DB, so this behavior
largely defeats vacuumdb's -j option.

Hence, invent options SKIP_DATABASE_STATS and ONLY_DATABASE_STATS
to allow applications to postpone vac_update_datfrozenxid() until the
end of a series of VACUUM requests, and teach vacuumdb to use them.

Per bug #17717 from Gunnar L.  Sadly, this answer doesn't seem
like something we'd consider back-patching, so the performance
problem will remain in v12-v15.

Tom Lane and Nathan Bossart

Discussion: https://postgr.es/m/17717-6c50eb1c7d23a886@postgresql.org
This commit is contained in:
Tom Lane
2023-01-06 14:17:25 -05:00
parent cd4b2334db
commit a46a7011b2
10 changed files with 147 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
src/include/commands/vacuum.h
View File

@@ -188,6 +188,8 @@ typedef struct VacAttrStats
#define VACOPT_SKIP_LOCKED 0x20 /* skip if cannot get lock */
#define VACOPT_PROCESS_TOAST 0x40 /* process the TOAST table, if any */
#define VACOPT_DISABLE_PAGE_SKIPPING 0x80 /* don't skip any pages */
#define VACOPT_SKIP_DATABASE_STATS 0x100 /* skip vac_update_datfrozenxid() */
#define VACOPT_ONLY_DATABASE_STATS 0x200 /* only vac_update_datfrozenxid() */
/*
* Values used by index_cleanup and truncate params.