| 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 14:31:07 |
| Message-ID: | AANLkTin49m4ZqzMAVMoaT21eR2QzVDkYLp=WD-OGyKY2@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Mar 14, 2011 at 10:25 AM, Alvaro Herrera
<alvherre(at)commandprompt(dot)com> wrote:
> Excerpts from Robert Haas's message of lun mar 14 11:18:24 -0300 2011:
>> On Mon, Mar 14, 2011 at 10:09 AM, Alvaro Herrera
>> <alvherre(at)commandprompt(dot)com> wrote:
>
>> > 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.
>
> Well, you only do multiple passes for tables that are really large, so
> it's precisely there that you want to save the extra overhead of having
> to do it multiple times.
Right but if the overhead is 0.0001% then who cares? I have no idea
what the real number is but it doesn't seem unrealistic to me that it
could be on that order.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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