Postgres FM24 Tammi 2025

Reads causing writes

Nikolay and Michael discuss a couple of surprising ways read queries (selects) can cause writes (shared buffers dirtied) in Postgres.

Here are some links to things they mentioned:

Reads causing writes in Postgres (post by Alex Jesipow) https://jesipow.com/blog/postgres-reads-cause-writes/
Exploring how SELECT queries can produce disk writes (post by Nikolay Sivko) https://blog.okmeter.io/postgresql-exploring-how-select-queries-can-produce-disk-writes-f36c8bee6b6f
Hint Bits (wiki) https://wiki.postgresql.org/wiki/Hint_Bits
pg_stat_statements https://www.postgresql.org/docs/current/pgstatstatements.html
pg_stat_kcache https://github.com/powa-team/pg_stat_kcache
pg_wait_sampling https://github.com/postgrespro/pg_wait_sampling
BUFFERS by default (episode 4!) https://postgres.fm/episodes/buffers-by-default
Page layout (docs) https://www.postgresql.org/docs/current/storage-page-layout.html
From Reddit (user merlinm), PD_ALL_VISIBLE may be a third case https://www.reddit.com/r/PostgreSQL/comments/1hjuyfn/comment/m3e6e7v/
Coroot https://coroot.com/

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What did you like or not like? What should we discuss next time? Let us know via a YouTube comment, on social media, or by commenting on our Google doc!

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Postgres FM is produced by:

Michael Christofides, founder of pgMustard
Nikolay Samokhvalov, founder of Postgres.ai

With special thanks to:

Jessie Draws for the elephant artwork

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