[Xapian-devel] [Xapian-commits] 10683: trunk/xapian-core/ trunk/xapian-core/common/ trunk/xapian-core/queryparser/ trunk/xapian-core/tests/

Richard Boulton richard at lemurconsulting.com
Thu Jun 5 07:21:27 BST 2008

Olly Betts wrote:
> On Wed, Jun 04, 2008 at 01:48:37PM +0100, richard wrote:
>> queryparser/queryparser.lemony: Fix various cases where queries
>> were constructed pair-wise within a loop, which leads to O(N*N)
>> scaling behaviour (because each intermediate query construction
>> is O(M) where M is the size of that query, and there are N of
>> them).
> Um, the real bug is in query construction then!  Pairwise construction
> shouldn't depend on the size of the subqueries (it used to, but I
> thought that had already been fixed).

I haven't looked at the code in any detail, but I think the problem is 
that each pairwise construction causes a full copy of the subquery 
(perhaps due to the simplification part of the construction).  Perhaps 
the end_construction() part needs to be made lazy to avoid calling this 
step repeatedly.

> That aside, it may be more efficient to build up subqueries in an array
> and construct the query object in one (as your patch does), particularly
> in the case where we're using new to create the query object.  But we
> really should fix this in Query, not just work around the issue in
> QueryParser.

The test for checking the behaviour of QueryParser should be applicable 
to Query with a few modifications, so we at least have an easy way to 
check the performance now. :)


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