Horton

Re: patch: SQL/MED(FDW) DDL

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Shigeru HANADA <hanada@metrosystems.co.jp>, Itagaki Takahiro <itagaki.takahiro@gmail.com>, Alvaro Herrera <alvherre@commandprompt.com>, SAKAMOTO Masahiko <sakamoto.masahiko@oss.ntt.co.jp>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2010-10-05T15:15:00Z
Lists: pgsql-hackers 
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