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Subject: Re: foreign data wrappers
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From: Zheng Yang <zhengyang4k@gmail.com>
In-Reply-To: <4D8E0125.9060905@dunslane.net>
Date: Tue, 29 Mar 2011 19:28:57 +0800
Cc: Shiv <rama.theone@gmail.com>, Selena Deckelmann <selena@chesnok.com>,
	Alvaro Herrera <alvherre@commandprompt.com>,
	Guillaume Lelarge <guillaume@lelarge.info>,
	pgsql-students <pgsql-students@postgresql.org>
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To: Andrew Dunstan <andrew@dunslane.net>

Hi guys,

>>=20
>> 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?
>=20
> 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.
>=20


Regarding the previous flickr example, I'm wondering how this 'free text =
search' function can be done if the FDW is blind to the SELECT =
statement.

For instance, the following query is to retrieve a photo relevant to =
'panda':

	SELECT photo FROM flickr_table WHERE search LIKE '%panda%';

In this case, the FDW can only open a connection to flickr web service =
and return the next 'row' .=20
The problem is that there are a huge number of photos in flickr server =
and retrieving them sequentially is not realistic.=20
Any ideas on how this can be done?


ZY=