Skip site navigation (1) Skip section navigation (2)

Re: So, is COUNT(*) fast now?

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: So, is COUNT(*) fast now?
Date: 2011-10-23 23:01:01
Message-ID: (view raw or whole thread)
Lists: pgsql-hackers
On Fri, Oct 21, 2011 at 12:52 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> Also, this line is kind of expensive:
>        if (!visibilitymap_test(scandesc->heapRelation,
>                                ItemPointerGetBlockNumber(tid),
>                                &node->ioss_VMBuffer))
> Around 2%.  But I don't see any way to avoid that, or even make it cheaper.

Could we cache by ItemPointerGetBlockNumber(tid) the results of those
tests, for groups of tids on the same index page?

How useful this would be would depend on how well-clustered the table
and index are.



In response to


pgsql-hackers by date

Next:From: Tom LaneDate: 2011-10-23 23:26:57
Subject: Re: EXECUTE tab completion
Previous:From: Jeff JanesDate: 2011-10-23 22:41:05
Subject: Index only scans and visibilitymap.c

Privacy Policy | About PostgreSQL
Copyright © 1996-2015 The PostgreSQL Global Development Group