Re: foreign data wrappers

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.fr
http://dalibo.com