1

I'm using the following query to find unused indexes:

SELECT 
PSUI.indexrelid::regclass AS IndexName 
,PSUI.relid::regclass AS TableName 
FROM pg_stat_user_indexes AS PSUI 
JOIN pg_index AS PI 
ON PSUI.IndexRelid = PI.IndexRelid 
WHERE PSUI.idx_scan = 0 
AND PI.indisunique IS FALSE;

Should I run any stats gathering syntax or anything else before running it? Is the above query OK for such purpose? I mean, then all indexes shown in the SQL output should be just deleted?

It's a 8 year old BD, so resulting rows may be actually left overs and, I guess there should be enough stats so tell wherever and is used or not.

2

Seems like a decent approach. Of course, one should apply some human verification to this before automatically dropping everything that seems unused. For example, it's conceivable that the statistics were recently reset and/or an index is only used for some occasional batch tasks.

  • Is it possible to know when where statistics reset? – Gonzalo Vasquez May 4 '16 at 13:23
  • 1
    You can check in pg_stat_database.stats_reset. This detects not only intentional resets, but also resets due to crashes or unclean shutdowns. Stats can also be reset on individual objects, but I don't think there is any way to see when/if that has happened. – jjanes May 4 '16 at 15:14

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