From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
Cc: | jd <jd(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Better estimates of index correlation |
Date: | 2011-03-14 14:18:24 |
Message-ID: | AANLkTi=d0aMohmr5zu8Lq0FEM_o0U8zWkxQKyWaO7Xqb@mail.gmail.com |
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On Mon, Mar 14, 2011 at 10:09 AM, Alvaro Herrera
<alvherre(at)commandprompt(dot)com> wrote:
> Excerpts from Joshua D. Drake's message of dom mar 13 23:20:01 -0300 2011:
>> On Sun, 2011-03-13 at 19:40 -0400, Tom Lane wrote:
>>
>> > I'm not planning to do anything about this idea right now, since I'm
>> > still hip-deep in collations, but I thought I'd throw it out to get
>> > it on the record.
>> >
>> > Comments?
>>
>> One question: Where is the overhead increase?
>
> During VACUUM, in the pass that processes indexes.
>
> I think Tom is sligthly confused though: AFAICT this must happen in
> btvacuumscan (which does the actual scan), not btvacuumcleanup (which
> may not do it, if btbulkdelete did it previously). Which means it would
> be done for each pass over the index when vacuuming a relation, because
> I don't see any way for this function to determine whether this is the
> last pass we'll do over the index.
>
> It sure would be nice to be able to do it only during the last scan.
Does it really matter? What Tom was describing sounded embarassingly cheap.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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