From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Shigeru HANADA <hanada@metrosystems.co.jp>
Cc: Itagaki Takahiro <itagaki.takahiro@gmail.com>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: SAKAMOTO Masahiko <sakamoto.masahiko@oss.ntt.co.jp>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: patch: SQL/MED(FDW) DDL
Date: Tue, 05 Oct 2010 18:15:00 +0300
Message-ID: <4CAB40F4.8030500@enterprisedb.com> (raw)
In-Reply-To: <AANLkTi=3KBbnKpRdmb7y_Ahmn9cms8khHk_V1kJ6FajT@mail.gmail.com>
References: <20100930164835.9FD2.6989961C@metrosystems.co.jp>
<AANLkTimat-AH84xsA+izMAdyBMDGTVMPYCg0XkNeDqfJ@mail.gmail.com>
<20101005211031.A022.6989961C@metrosystems.co.jp>
<23621.1286288719@sss.pgh.pa.us>
<AANLkTinE5-WV_jEfUOm2ug0QcQNtFLBQSiCaT8A-NDgg@mail.gmail.com>
<23958.1286289686@sss.pgh.pa.us>
<AANLkTi=3KBbnKpRdmb7y_Ahmn9cms8khHk_V1kJ6FajT@mail.gmail.com>
On 05.10.2010 17:56, Robert Haas wrote:
> On Tue, Oct 5, 2010 at 10:41 AM, Tom Lane<tgl@sss.pgh.pa.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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To: pgsql-hackers@postgresql.org
Cc: heikki.linnakangas@enterprisedb.com, robertmhaas@gmail.com, tgl@sss.pgh.pa.us, hanada@metrosystems.co.jp, itagaki.takahiro@gmail.com, alvherre@commandprompt.com, sakamoto.masahiko@oss.ntt.co.jp
Subject: Re: patch: SQL/MED(FDW) DDL
In-Reply-To: <4CAB40F4.8030500@enterprisedb.com>
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