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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: Andrew Dunstan <andrew(at)dunslane(dot)net>, Shiv <rama(dot)theone(at)gmail(dot)com>, Selena Deckelmann <selena(at)chesnok(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, pgsql-students <pgsql-students(at)postgresql(dot)org>
Subject: Re: foreign data wrappers
Date: 2011-03-29 15:48:53
Message-ID: 4D91FF65.2090401@lelarge.info (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-students
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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