Re: [bdbxml] Paging/controlling result set?

Antony Grinyer wrote:
> We run queries on a large container that potentially brings back 
> hundreds of thousands of results from XQueries. We get 
> BDBXML:allocate():Out of memory errors, which I'm sure is because we're 
> trying to collect these results all at one in a StringBuffer (not 
> good!). Is there any way in DB XML to control the result set coming 
> back? e.g. caching or paging, so the user is not presented with 
> thousands of results at one time?

The best way to acheive a paging effect is to use lazy evaluation. You 
set this on the XmlQueryContext object:

http://www.sleepycat.com/xmldocs/java/com/sleepycat/dbxml/XmlQueryContext.html#setEvaluationType(int)

Then when you are iterating through the XmlResults object, make sure 
that you delete each returned XmlValue object as soon as possible. This 
will make sure that DB XML uses the least amount of memory possible 
during it's query.

In order to page, you can then return as many results as you need from 
the XmlResults object, and then store it somewhere until you want to get 
some more results from it.

> Also, does the DB XML caching 
> environment property increase performance? Our environment is set with:

Performance with relation to the Environment is a very large discussion. 
You will find information regarding it in the documentation:

http://www.sleepycat.com/docs/ref/toc.html#env

John

-- 
John Snelson, Berkeley DB XML Engineer
Sleepycat Software, Inc
http://www.sleepycat.com

Contracted to Sleepycat through Parthenon Computing Ltd
http://blog.parthcomp.com/dbxml


------------------------------------------
To remove yourself from this list, send an
email to [email protected]