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postgres_query_cache_hit_ratio.sql
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--
-- Author: Hari Sekhon
-- Date: 2020-08-05 16:22:42 +0100 (Wed, 05 Aug 2020)
--
-- vim:ts=4:sts=4:sw=4:et:filetype=sql
--
-- https://github.com/HariSekhon/SQL-scripts
--
-- License: see accompanying Hari Sekhon LICENSE file
--
-- If you're using my code you're welcome to connect with me on LinkedIn and optionally send me feedback to help steer this or other code I publish
--
-- https://www.linkedin.com/in/HariSekhon
--
-- PostgreSQL queries cache-hit ratio from pg_stat_statements
--
-- Requires PostgreSQL 9.1+
--
-- Tested on PostgreSQL 9.1+, 10.x, 11.x, 12.x, 13.0
-- postgresql.conf needs before start:
-- shared_preload_libraries = 'pg_stat_statements'
--
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
SELECT
calls,
rows,
shared_blks_hit,
shared_blks_read,
-- using greatest() to avoid divide by zero error, by ensuring we divide by at least 1
shared_blks_hit /
GREATEST(shared_blks_hit + shared_blks_read, 1)::float AS shared_blks_hit_ratio,
-- casting divisor to float to avoid getting integer maths returning zeros instead of fractional ratios
local_blks_hit,
local_blks_read,
local_blks_hit /
GREATEST(local_blks_hit + local_blks_read, 1)::float AS local_blks_hit_ratio,
query
FROM
pg_stat_statements
--ORDER BY rows DESC
ORDER BY
shared_blks_hit_ratio DESC,
local_blks_hit_ratio DESC,
rows DESC
LIMIT 100;