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From: Guillaume Lelarge <guillaume@lelarge.info>
To: Zheng Yang <zhengyang4k@gmail.com>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Shiv <rama.theone@gmail.com>
Cc: Selena Deckelmann <selena@chesnok.com>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: pgsql-students <pgsql-students@postgresql.org>
Subject: Re: foreign data wrappers
Date: Tue, 29 Mar 2011 17:48:53 +0200
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Le 29/03/2011 13:28, Zheng Yang a écrit :
> Hi guys,
> 
>>>
>>> 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?
>>
>> 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.
>>
> 
> 
> 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' . 
> The problem is that there are a huge number of photos in flickr server and retrieving them sequentially is not realistic. 
> Any ideas on how this can be done?
> 

It probably means that flickr is not a good example of a nice fdw.


-- 
Guillaume
 http://www.postgresql.fr
 http://dalibo.com



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