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Re: foreign data wrappers

From: Guillaume Lelarge <guillaume(at)lelarge(dot)info>
To: Zheng Yang <zhengyang4k(at)gmail(dot)com>
Cc: Selena Deckelmann <selena(at)chesnok(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, pgsql-students(at)postgresql(dot)org
Subject: Re: foreign data wrappers
Date: 2011-03-24 07:54:42
Message-ID: (view raw or whole thread)
Lists: pgsql-generalpgsql-students

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
I hope he'll publish his slides somewhere really soon :)

> 3) in one of the examples, when declaring an FDW,  "..LIBRARY ’’ LANGUAGE C;"  the LANGUAGE option is going to be C only?

According to, 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.


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