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Re: SHOULD use POST for expensive queries?

From: Kendall Clark <kendall@monkeyfist.com>
Date: Wed, 18 Jan 2006 13:58:47 -0500
Message-Id: <4156D2F7-A2BD-4B45-B5DA-9DF4933FFB8C@monkeyfist.com>
Cc: dawg mailing list <public-rdf-dawg@w3.org>
To: Steve Harris <S.W.Harris@ecs.soton.ac.uk>


On Jan 18, 2006, at 12:18 PM, Steve Harris wrote:

>> Actually, now that I think about it, that's not *entirely* true. Real
>> (as opposed to toy) database cost models include table size, and even
>> for arbitrary 3rd party graphs, with clever caching and use of HTTP,
>> a SPARQL query analyzer could make some good guesses (so, imagine the
>> ideal case: all the graphs are cached locally and known to be fresh),
>> so it's not as bad as I made it seem.
>
> It's not even that easy, without running the main part of the query  
> for
> real it's not possibly to calculate how much effort will be  
> required to
> satisfy the OPTIONAL blocks or how many UNION branches you will  
> have to
> take. My estimation code assumes worst-ish cases for those, which  
> is often
> not accurate.

Absolutely! My point was just in re: assembling RDF datasets. That's  
only part of a cost model for query analysis, as you point out. :>

>> But in the common or pathological cases (where all graphs are
>> unknown, uncached, and have to be retrieved from arbitrary origin
>> servers), well... -shudder-.
>
> Quite.

It's ugly, yes -- but better ugly than impossible, I think.

Cheers,
Kendall
Received on Wednesday, 18 January 2006 18:58:58 GMT

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