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Re: foreign data wrappers

From: Zheng Yang <zhengyang4k(at)gmail(dot)com>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
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: 2011-03-27 12:51:21
Message-ID: E7108617-4213-4C33-B5C8-D510B65EC34D@gmail.com (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-students
Hi,

I managed to clone a copy of 9.1devel and compiled an binary from it. I also did a make in the 'contrib/file_fdw/' folder and a file_fdw.so file is generated.

But the following error occurs when I was trying to experiment with the file FDW:

postgres=# CREATE FUNCTION file_fdw_handler() RETURNS fdw_handler AS 'file_fdw' LANGUAGE C STRICT;
ERROR:  could not access file "file_fdw": No such file or directory
STATEMENT:  CREATE FUNCTION file_fdw_handler() RETURNS fdw_handler AS 'file_fdw' LANGUAGE C STRICT;
ERROR:  could not access file "file_fdw": No such file or directory


Did I miss anything?


ZY



On 26-Mar-2011, at 11:07 PM, Andrew Dunstan wrote:

> 
> 
> 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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