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Re: show Heap Fetches in EXPLAIN for index-only scans

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: show Heap Fetches in EXPLAIN for index-only scans
Date: 2012-01-13 15:31:42
Message-ID: CA+TgmobfkaFay-4cd-d6AqJ1rEtNFAmBhky7KT54d8xWe3gyVA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Jan 13, 2012 at 10:29 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> On Fri, Jan 13, 2012 at 16:21, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I think that people who are using index-only scans are going to want
>> some way to find out the degree to which the scans are in fact
>> index-only.
>>
>> So here's a 5-line patch that adds the number of heap fetches to the
>> EXPLAIN ANALYZE output.  This might not be all the instrumentation
>> we'll ever want here, but I think we at least want this much.
>
> Agreed.
>
> Would also be good to have counter sin pg_stat_* for this, since you'd
> usually want to look at this kind of data over time as well. In your
> plans? ;)

Not really.  I don't have a clear enough idea about what that should
look like, and I expect a vigorous debate over the distributed cost of
another counter.  But I'm happy to have someone who feels more
strongly about it than I do take up the cause.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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