Performance cliffs

Postgres FM

Nikolay and Michael are joined by Tomas Vondra to discuss single query performance cliffs — what they are, why they happen, some things we can do to make them less likely or less severe, and some potential improvements to Postgres that could help.
Here are some links to things they mentioned:

• Tomas Vondra https://postgres.fm/people/tomas-vondra
• Where do performance cliffs come from? (Talk by Tomas) https://www.youtube.com/watch?v=UzdAelm-QSY
• Where do performance cliffs come from? (Slides) https://vondra.me/pdf/performance-cliffs-posette-2024.pdf
• Increase the number of fast-path lock slots (committed for Postgres 18) https://www.postgresql.org/message-id/flat/E1ss4gX-000IvX-63%40gemulon.postgresql.org
• San Francisco Bay Area Postgres meet-up with Tomas on 8th April (online) https://www.meetup.com/postgresql-1/events/306484787
• Our episode on Extended Statistics https://postgres.fm/episodes/extended-statistics
• Logging plan of the currently running query (proposed patch by Rafael Thofehrn Castro and Atsushi Torikoshi) https://commitfest.postgresql.org/patch/5330
• Our episode with Peter Geoghegan on Skip Scan https://postgres.fm/episodes/skip-scan
• Index Prefetching patch that Tomas is collaborating with Peter Geoghegan on https://commitfest.postgresql.org/patch/4351
• A generalized join algorithm, G-Join (paper by Goetz Graefe) https://dl.gi.de/server/api/core/bitstreams/ce8e3fab-0bac-45fc-a6d4-66edaa52d574/content
• Smooth Scan: Robust Access Path Selection without Cardinality Estimation (paper by R. Borovica, S. Idreos, A. Ailamaki, M. Zukowski, C. Fraser) https://stratos.seas.harvard.edu/sites/g/files/omnuum4611/files/stratos/files/smoothscan.pdf
• Just-in-Time Compilation (JIT) https://www.postgresql.org/docs/current/jit.html
• Notes from a pgconf.dev unconference session in 2024 about JIT (discusses issues) https://wiki.postgresql.org/wiki/PGConf.dev_2024_Developer_Unconference#JIT_compilation
• Implementing an alternative JIT provider for PostgreSQL (by Xing Guo) https://higuoxing.com/archives/implementing-jit-provider-for-pgsql
• Tomas’ Office Hours https://vondra.me/posts/office-hours-experiment

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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