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Re: Optimizer and Indexes with Joins

From: Frank Bax <fbax(at)sympatico(dot)ca>
To: "Hargis" <ljhargis(at)vcn(dot)com>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Optimizer and Indexes with Joins
Date: 2002-03-05 17:59:46
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-novice
Sorry, you can't tell pg what index to use.

You can usually get pg to use your indexes by changes to query and/or 
schema.  If you post a new message to list, that says "why isn't this query 
using index7?", and then include:

1) A copy of your query
2) The output of "explain <query>"
3) schema (you can use "pg_dump -s -t <table> <database>" for each table in 

The explanations/suggestions provided by others will quickly teach you a 
lot about how pg works in your environment.


At 10:01 PM 04/03/02 -0700, Hargis wrote:
>I have a question regarding the optimizer and indexes.   Having a boss 
>that is fluent in data flex but trying to understand postgresql, I am 
>trying to find out if postgresql has a way to basically tell the optimizer 
>which index to use.  The boss states that in data flex you "tell" it to 
>use index 7 and it uses index 7.
>We utilize vacuum analyze and we also structure our where clauses to fit 
>the specific indexes.  Further, we set the "enable sequence scan" to off 
>and it did not improve any performace issues.  Most of our selects are 
>"joins" though and that may be causing most of our performance 
>issues.  Any advice out there?
>If I need to provide any further information, please advise....
>LA Hargis
>(Trying to get better at postgres)

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