Tom Lane a46a7011b2 Add options to control whether VACUUM runs vac_update_datfrozenxid. ... 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		2023-01-06 14:17:25 -05:00
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src	Add options to control whether VACUUM runs vac_update_datfrozenxid.	2023-01-06 14:17:25 -05:00
KNOWN_BUGS
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MISSING_FEATURES
TODO