| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Shigeru HANADA <hanada(at)metrosystems(dot)co(dot)jp>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, SAKAMOTO Masahiko <sakamoto(dot)masahiko(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: patch: SQL/MED(FDW) DDL |
| Date: | 2010-10-05 14:27:03 |
| Message-ID: | AANLkTinE5-WV_jEfUOm2ug0QcQNtFLBQSiCaT8A-NDgg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Oct 5, 2010 at 10:25 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Shigeru HANADA <hanada(at)metrosystems(dot)co(dot)jp> writes:
>> Can we treat statistics of a foreign table separately?
>
>> 1. Same as local tables (maybe required)
>> (pg_statistic.*, pg_class.reltuples/relpages)
>
> This whole discussion seems to me to be about trying to do things outside
> the FDW that should properly be left inside the FDW. Who's to say that
> the remote side even *has* statistics of the sort that PG creates?
>
> We should provide an API that lets the FDW return a cost estimate for a
> proposed access path. Where it gets the cost estimate from is not
> something that should be presupposed.
Unless there's some way for the FDW to have local tables for caching
its statistics, the chances of this having decent performance seem to
be near-zero.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company
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