added postgres_indexes_caches_hit_ratio.sql

sql/postgres_indexes_caches_hit_ratio.sql

@@ -0,0 +1,27 @@
+--
+--  Author: Hari Sekhon
+--  Date: 2020-08-05 15:28:12 +0100 (Wed, 05 Aug 2020)
+--
+--  vim:ts=2:sts=2:sw=2:et:filetype=sql
+--
+--  https://github.com/harisekhon/bash-tools
+--
+--  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 Indexes Cache-hit Ratio
+--
+-- should be closer to 1, eg. 0.99
+
+SELECT
+  SUM(idx_blks_read) AS idx_read,
+  SUM(idx_blks_hit)  AS idx_hit,
+  (SUM(idx_blks_hit) - SUM(idx_blks_read)) /
+					SUM(idx_blks_hit)
+							AS ratio
+FROM
+  pg_statio_user_indexes;