From: Guillaume Lelarge <guillaume@lelarge.info>
To: Zheng Yang <zhengyang4k@gmail.com>
Cc: Selena Deckelmann <selena@chesnok.com>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: pgsql-students@postgresql.org
Subject: Re: foreign data wrappers
Date: Thu, 24 Mar 2011 08:54:42 +0100
Message-ID: <4D8AF8C2.3000007@lelarge.info> (raw)
In-Reply-To: <3EF9E4CC-CF42-4B45-86FF-4CB9D46D7442@gmail.com>
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<AANLkTimKc4Jb4ydk=GO3shdv0gTPyad+y9z_kXXVKZoq@mail.gmail.com>
<4D879CD0.5030803@dunslane.net>
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<3EF9E4CC-CF42-4B45-86FF-4CB9D46D7442@gmail.com>
Hi,
Le 24/03/2011 06:39, Zheng Yang a écrit :
> [...]
> I've figured out what a FDW does. It's quite clear from the doc that a FDW is an interface postgresql database used to communicate with
> other data sources either it be a file, another DBMS or even weblinks (please correct me if i am wrong).
>
You're right.
> I have a few more specific questions on FDW. hope you guys can help!
>
> 1) by right the FDW should be implemented by the vendor of the datasource, is that correct?
>
If you mean that an Oracle FDW should be implemented by Oracle, and an
Excel FDW should be implemented by Microsoft, then no, I don't think so.
AFAICS, anyone can write any FDW.
> 2) what are the FDW that has been implemented? I've seen an plain file FWD module from the link provided by selena.
>
Yeah, that's the one provided as a contrib module. I've also seen a
postgres one and a twitter one on pgsql-hackers. Andrew wrote two other
FDWs he'll talk about today at PGEast
(http://people.planetpostgresql.org/andrew/index.php?/archives/163-First-extension.html).
I hope he'll publish his slides somewhere really soon :)
> 3) in one of the examples, when declaring an FDW, "..LIBRARY ’foosql_fdw.so’ LANGUAGE C;" the LANGUAGE option is going to be C only?
>
According to
http://developer.postgresql.org/pgdocs/postgres/fdwhandler.html, yes.
> 4) Is theFDW something similar to the Mysql storage engine architecture?
>
Not really.
> 5) for the datalink, the doc has mentioned about it's going to be OS dependent. but i dun quite understand how does the kernel module and LD_PRELOAD will work in this case, esp.LD_PRELOAD.
>
No idea.
Writing some FDWs would make a really good GSoC project.
--
Guillaume
http://www.postgresql.frhttp://dalibo.com
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Cc: guillaume@lelarge.info, zhengyang4k@gmail.com, selena@chesnok.com, andrew@dunslane.net, pgsql-students@postgresql.org
Subject: Re: foreign data wrappers
In-Reply-To: <4D8AF8C2.3000007@lelarge.info>
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