postgres_tables_cache_hit_ratio.sql

--
--  Author: Hari Sekhon
--  Date: 2020-08-05 14:57:37 +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
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--  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
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--  https://www.linkedin.com/in/HariSekhon
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-- PostgreSQL Tables Cache-hit Ratio
--
-- should be closer to 1, eg. 0.99, at least 0.90
--
-- otherwise increase 'shared_buffer' size (should be at least 25% of total RAM for a dedicated DB server)
--
-- Tested on PostgreSQL 8.4, 9.x, 10.x, 11.x, 12.x, 13.0

SELECT
    SUM(heap_blks_read) AS heap_blks_read,
    SUM(heap_blks_hit)  AS heap_blks_hit,
             SUM(heap_blks_hit) /
    GREATEST(SUM(heap_blks_hit) + SUM(heap_blks_read), 1)::float
                  AS ratio
FROM
    pg_statio_user_tables;