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From Andy Seaborne <>
Subject Re: Problems with TDB Optimizer
Date Mon, 04 Apr 2011 19:43:04 GMT
Just joining up the threads for the archive:


on the jena-users list

On 01/04/11 19:44, Bill Roberts wrote:
> I've come across some unexpected (to me!) behaviour of the TDB Optimizer and wondering
if someone could shed any light on it.
> For our database, (around 30 million triples, 350-odd different predicates, around 50
named graphs, using UnionDefaultGraph - everything is in a named graph), we've found that
including the stats.opt file makes some queries significantly slower than having no optimizer.
> Some relatively complex queries run quite quickly and probably a bit quicker with optimization
than without.  But in other cases,  quite simple queries  run a lot slower - maybe 10 or 20
times slower with stats.opt in place than they do without it.
> Is this known behaviour?
> Here's an example:
> SELECT ?key ?label WHERE {<a-specific-uri>  ?p ?key . ?key<>
 ?label }
> This query took around 30 seconds with stats.opt in place, and less than 2 seconds without
it. (Some of that 2 seconds would have been HTTP transfer and web page rendering time).
> We're currently running TDB 0.8.9 and Joseki 3.4.3 on 64 bit Ubuntu.  (Though I've found
similar behaviour on 32-bit Ubuntu with slightly older versions of TDB and Joseki).
> Thanks!
> Bill

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