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Re: Unused indexes - PostgreSQL 9.2 - Mailing list pgsql-general

From Lucas Possamai
Subject Re: Unused indexes - PostgreSQL 9.2
Date
Msg-id CAE_gQfX+90LQZqejgEWaLTAChLWuZia42_xEXaNB=9GhVmKqrw@mail.gmail.com
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In response to Re: Unused indexes - PostgreSQL 9.2  (Melvin Davidson <melvin6925@gmail.com>)
Responses Re: Unused indexes - PostgreSQL 9.2
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Sorry, I was too busy looking at the content.

Has the size / # rows changed recently? If the planner thinks it can load all the rows faster, it will use a seqscan  regardless if you have an index.

If that is the case, you can force index use by doing a

SET enable_seqscan = off  

before executing the query.

Hmm... ok... but the situation is:

1 - I dropped the index
2 - Found a very slow query
3 - The "WHERE" clause was using the index that I've just dropped
4 - I ran the query in my test environment (Same DB as prod) with explain analyze to see if the query was indeed using the index I've dropped
5 - Yes, the query was using the index
6 - re-created the index

7 - The total time went from 2000ms to 200ms

So, I don't think the index was indeed not being used.
I believe the stats are not working, just don't know how to confirm that, as I have nothing on my logs

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