Re: hot updates and fillfactor

From: Aleksander Alekseev <aleksander(at)timescale(dot)com>
To: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Cc: Fabrice Chapuis <fabrice636861(at)gmail(dot)com>
Subject: Re: hot updates and fillfactor
Date: 2024-03-19 10:17:23
Message-ID: CAJ7c6TM+rhPML39gNa0rkA9qBWWSGBg4Uf1P05Qhvtm991N4QA@mail.gmail.com
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Hi Fabrice,

> I do not understand why hot_updates value is not 0 for pg_database? Given that reloptions is empty for this table that means it has a default value of 100%

Maybe I didn't entirely understand your question, but why would you
assume they are somehow related?

According to the documentation [1][2]:

pg_class.reloptions:
Access-method-specific options, as “keyword=value” strings

pg_stat_all_tables.n_tup_hot_upd:
Number of rows HOT updated. These are updates where no successor
versions are required in indexes.

The value of n_tup_hot_upd is not zero because there are tuples that
were HOT-updated. That's it. You can read more about HOT here [3].

[1]: https://www.postgresql.org/docs/current/catalog-pg-class.html
[2]: https://www.postgresql.org/docs/current/monitoring-stats.html
[3]: https://www.postgresql.org/docs/current/storage-hot.html

--
Best regards,
Aleksander Alekseev

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