From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Shigeru HANADA <hanada(at)metrosystems(dot)co(dot)jp>, 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 15:15:00 |
Message-ID: | 4CAB40F4.8030500@enterprisedb.com |
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Lists: | pgsql-hackers |
On 05.10.2010 17:56, Robert Haas wrote:
> On Tue, Oct 5, 2010 at 10:41 AM, Tom Lane<tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> (I'd also say that your performance estimate is miles in advance of any
>> facts; but even if it's true, the caching ought to be inside the FDW,
>> because we have no clear idea of what it will need to cache.)
>
> I can't imagine how an FDW could possibly be expected to perform well
> without some persistent local data storage. Even assume the remote
> end is PG. To return a cost, it's going to need the contents of
> pg_statistic cached locally, for each remote table. Do you really
> think it's going to work to incur that overhead once per table per
> backend startup?
It doesn't seem completely out of the question to me. Sure, it's
expensive, but it's only incurred the first time a remote table is
accessed in a session. Local persistent storage would be nice, but a lot
of applications might prefer to not use it anyway, to ensure that fresh
statistics are used.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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