text: --
  --  Author: Hari Sekhon
  --  Date: 2020-08-05 14:57:37 +0100 (Wed, 05 Aug 2020)
  --
  --  vim:ts=2:sts=2:sw=2:et:filetype=sql
  --
  --  https://github.com/harisekhon/sql
  --
  --  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 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;
  