From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Marko Tiikkaja <marko(at)joh(dot)to> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: get_actual_variable_range vs idx_scan/idx_tup_fetch |
Date: | 2014-10-17 21:59:13 |
Message-ID: | 10389.1413583153@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Marko Tiikkaja <marko(at)joh(dot)to> writes:
> On 10/17/14, 11:47 PM, Tom Lane wrote:
>> Marko Tiikkaja <marko(at)joh(dot)to> writes:
>>> So what I'd like to have is a way to be able to distinguish between
>>> indexes being used to answer queries, and ones being only used for stats
>>> lookups during planning.
>> Why? Used is used.
> Because I don't need a 30GB index on foo(a,b,c) to look up statistics.
> If I ever have a problem, I can replace it with a 5GB one on foo(a).
Well, the index might've been getting used in queries too in a way that
really only involved the first column. I think you're solving the wrong
problem here. The right problem is how to identify indexes that are
being used in a way that doesn't exploit all the columns. Which is not
necessarily wrong in itself --- what you'd want is to figure out when the
last column(s) are *never* used. The existing stats aren't terribly
helpful for that, I agree.
regards, tom lane
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