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Date: Tue, 08 Nov 2005 10:11:40 +0100
From: Marcel Reutegger <marcel.reutegger@gmx.net>
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To: jackrabbit-dev@incubator.apache.org
Subject: Re: How to limit the nodes amount with xpath query returned
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Hi Yao,

Yao Harrison wrote:
>    Sure, my question is the same as you thought, and I was agreed with
> your opinion that the paging of query result should be the scope of
> applications , but imagine that  you have to filter the more than ten
> thousands nodes and pick up only 10 objects in it as your hoped every
> times  ,  so  we should queried for this big result set every time and
> get the small set of query returned only , and this will take the
> defect of the application's performance.

not necessarily, an implementation should be able to handle this 
scenario. the jcr api allows to lazy instanciate result nodes and a 
client application may skip results (NodeIterator.skip()) to avoid 
stepping through e.g. 10000 nodes to find the one it is interested in.

I have to admit, that the current query handler implementation in 
jackrabbit only takes some advantage of this fact. query results are 
always calculated as a whole in respect to the uuids of the result node. 
the actual result node instances however are fetched on a lazy basis.

There was another thread about a similar topic:
http://thread.gmane.org/gmane.comp.apache.jackrabbit.devel/3602

so, there's still room for improvement.

>   So , I hope to limit the result set amount when query executed and 
> returned , just like MySQL's " Limit " statment.

This would be a proprietary extension, and I don't know how you would 
specify such a keyword in XPath.

regards
marcel