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Re: foreign data wrappers

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Zheng Yang <zhengyang4k(at)gmail(dot)com>
Cc: Shiv <rama(dot)theone(at)gmail(dot)com>, Selena Deckelmann <selena(at)chesnok(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Guillaume Lelarge <guillaume(at)lelarge(dot)info>, pgsql-students <pgsql-students(at)postgresql(dot)org>
Subject: Re: foreign data wrappers
Date: 2011-03-26 15:07:17
Message-ID: 4D8E0125.9060905@dunslane.net (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-students

On 03/24/2011 10:07 PM, Zheng Yang wrote:
>
>
> I've briefly gone through the slides. Regarding the 6 callbacks, is 
> that correct to say that a full table scan will always be performed 
> irregardless of the sql statement,
> the FDW is blind to the sql query performed, right?

Yes, fairly much. If the feed is large you need some way to pass a limit 
to the foreign side, possibly via table options. I'm fairly sure you 
won't be able to get it via the SELECT statement.

>
> And can anyone help explain what a planner is? What does this "provide 
> cost estimates to planner" mean? Thanks!


See <http://www.postgresql.org/docs/current/static/planner-optimizer.html>

If you're going to work on PostgreSQL code you need to read the docs.

cheers

andrew


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