Slow count

Postgres FM

Nikolay and Michael discuss why counting can be slow in Postgres, and what the options are for counting things quickly at scale.
Here are some links to things they mentioned:

• Aggregate functions (docs) https://www.postgresql.org/docs/current/functions-aggregate.html
• PostgREST https://github.com/PostgREST/postgrest
• Get rid of count by default in PostgREST https://github.com/PostgREST/postgrest/issues/273
• Faster PostgreSQL Counting (by Joe Nelson on the Citus blog) https://www.citusdata.com/blog/2016/10/12/count-performance
• Our episode on Index-Only Scans https://postgres.fm/episodes/index-only-scans
• Postgres HyperLogLog https://github.com/citusdata/postgresql-hll
• Our episode on Row estimates https://postgres.fm/episodes/row-estimates
• Our episode about dangers of NULLs https://postgres.fm/episodes/nulls-the-good-the-bad-the-ugly-and-the-unknown
• Aggregate expressions, including FILTER https://www.postgresql.org/docs/current/sql-expressions.html#SYNTAX-AGGREGATES
• Spread writes for counter cache (tip from Tobias Petry) https://x.com/tobias_petry/status/1475870220422107137
• pg_ivm extension (Incremental View Maintenance) https://github.com/sraoss/pg_ivm
• pg_duckdb announcement https://motherduck.com/blog/pg_duckdb-postgresql-extension-for-duckdb-motherduck
• Our episode on Queues in Postgres https://postgres.fm/episodes/queues-in-postgres
• Our episode on Real-time analytics https://postgres.fm/episodes/real-time-analytics
• ClickHouse acquired PeerDB https://clickhouse.com/blog/clickhouse-acquires-peerdb-to-boost-real-time-analytics-with-postgres-cdc-integration
• Timescale Continuous Aggregates https://www.timescale.com/blog/materialized-views-the-timescale-way
• Timescale editions https://docs.timescale.com/about/latest/timescaledb-editions
• Loose indexscan https://wiki.postgresql.org/wiki/Loose_indexscan

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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