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Subject: Re: foreign data wrappers
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From: Zheng Yang <zhengyang4k@gmail.com>
In-Reply-To: <AANLkTi=0KD_ef9XDJde52nb0n5YgysMHTjWwkKZurDR-@mail.gmail.com>
Date: Thu, 24 Mar 2011 13:39:45 +0800
Cc: pgsql-students@postgresql.org
Message-Id: <3EF9E4CC-CF42-4B45-86FF-4CB9D46D7442@gmail.com>
References: <AANLkTi=FhaO5mX_YdqqsF1Yh0YNEHW8H1f0AUdpE0Fmo@mail.gmail.com>
	<690867AB-C50B-4354-91D0-8A0811639C4C@gmail.com>
	<AANLkTimKc4Jb4ydk=GO3shdv0gTPyad+y9z_kXXVKZoq@mail.gmail.com>
	<4D879CD0.5030803@dunslane.net>
	<AANLkTi=0KD_ef9XDJde52nb0n5YgysMHTjWwkKZurDR-@mail.gmail.com>
To: Selena Deckelmann <selena@chesnok.com>,
	Andrew Dunstan <andrew@dunslane.net>


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Hi guys,

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).

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?=20

2) what are the FDW that has been implemented? I've seen an plain file =
FWD module from the link provided by selena.

3) in one of the examples, when declaring an FDW,  "..LIBRARY =
=92foosql_fdw.so=92 LANGUAGE C;"  the LANGUAGE option is going to be C =
only?

4) Is theFDW something similar to the Mysql storage engine architecture?

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.

That's the question so far. Thanks very much!

Regards,
Zheng Yang


On 22-Mar-2011, at 3:49 AM, Selena Deckelmann wrote:

> On Mon, Mar 21, 2011 at 11:45 AM, Andrew Dunstan <andrew@dunslane.net> =
wrote:
>=20
>> Yes, but 9.1 *has* actual FDWs. The best thing to do (other than =
attending
>> my talk on Thursday :-) )
>=20
> :) I'll be around, so hopefully I can attend your talk and post up =
some notes!
>=20
>> is to look at the file_fdw module in git head, to
>> see an actual working example.
>=20
> I figured if I posted some wrong information someone would respond! :)
>=20
> Zheng - here is a link to the existing code:
> =
http://git.postgresql.org/gitweb?p=3Dpostgresql.git;a=3Dtree;f=3Dcontrib/f=
ile_fdw
>=20
> -selena
>=20
> --=20
> http://chesnok.com


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<html><head></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi =
guys,<div><br></div><div>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</div><div>other data sources either it be a file, =
another DBMS or even weblinks &nbsp;(please correct me if i am =
wrong).</div><div><br></div><div>I have a few more specific questions on =
FDW. hope you guys can help!</div><div><br></div><div>1) by right the =
FDW should be implemented by the vendor of the datasource, is that =
correct?&nbsp;</div><div><br></div><div>2) what are the FDW that has =
been implemented? I've seen an plain file FWD module from the link =
provided by selena.</div><div><br></div><div>3) in one of the examples, =
when declaring an FDW, &nbsp;"..<span class=3D"Apple-style-span" =
style=3D"font-size: 11px; ">LIBRARY =92foosql_fdw.so=92&nbsp;</span><span =
class=3D"Apple-style-span" style=3D"font-size: 11px; ">LANGUAGE =
C;</span>" &nbsp;the LANGUAGE option is going to be C =
only?</div><div><br></div><div>4) Is theFDW something similar to the =
Mysql storage engine architecture?</div><div><br></div><div>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.</div><div><br></div><div>That's the =
question so far. Thanks very =
much!</div><div><br></div><div>Regards,</div><div>Zheng =
Yang</div><div><br></div><div><br></div><div><br><div><div>On =
22-Mar-2011, at 3:49 AM, Selena Deckelmann wrote:</div><br =
class=3D"Apple-interchange-newline"><blockquote type=3D"cite"><div>On =
Mon, Mar 21, 2011 at 11:45 AM, Andrew Dunstan &lt;<a =
href=3D"mailto:andrew@dunslane.net">andrew@dunslane.net</a>&gt; =
wrote:<br><br><blockquote type=3D"cite">Yes, but 9.1 *has* actual FDWs. =
The best thing to do (other than attending<br></blockquote><blockquote =
type=3D"cite">my talk on Thursday :-) )<br></blockquote><br>:) I'll be =
around, so hopefully I can attend your talk and post up some =
notes!<br><br><blockquote type=3D"cite">is to look at the file_fdw =
module in git head, to<br></blockquote><blockquote type=3D"cite">see an =
actual working example.<br></blockquote><br>I figured if I posted some =
wrong information someone would respond! :)<br><br>Zheng - here is a =
link to the existing code:<br><a =
href=3D"http://git.postgresql.org/gitweb?p=3Dpostgresql.git;a=3Dtree;f=3Dc=
ontrib/file_fdw">http://git.postgresql.org/gitweb?p=3Dpostgresql.git;a=3Dt=
ree;f=3Dcontrib/file_fdw</a><br><br>-selena<br><br>-- =
<br>http://chesnok.com<br></div></blockquote></div><br></div></body></html=
>=

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