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NOEXPAND hints and bind-parameters [message #781007] Thu, 19 January 2012 13:47 Go to next message
Rich MacDonald is currently offline Rich MacDonald
Messages: 18
Registered: December 2010
Junior Member
Fascinating problem I am running into with eclipselink (2.2.1) and SQLServer. I am dealing with a "bill-of-materials" (BOM) query problem, so I have written a database view to do that query, then mapped the view to a JPA class. Then I use a named JPA query to access the query.

I noticed performance was heading downhill, so I ran the SQLServer profiler and tuning advisor. Lo and behold, the analysis stated that the BOM query could not be optimized because it included the NOEXPAND hint. So every query was running a full scan of the view then performing the filter afterwards. Queries run with the sqlserver management studio that take 1 second are now taking 1 minute when run with eclipselink/jdbc.

The NOEXPAND hint is either present or missing (no way to turn it off) so I have to find who is adding it, then stop it.

I can find no evidence in the trace log that the NOEXPAND hint is present. So it could be some problem with the trace/analysis tool. Unlikely but possible.

I walked the eclipselink code in the debugger as far as I could and did not see anything setting a query hint.

I tried some other alternatives. I rewrote the named JPA query as a named native query. Same problem.

I tried the criteria api. Same problem.

I bypassed the named queries by generating the sql on the fly and creating a native query that way. This worked! SQLserver no longer "sees" a NOEXPAND hint and optimizes the query properly.

When I set eclipselink.jdbc.bind-parameters to false, it works! Bingo.

What gives?
Re: NOEXPAND hints and bind-parameters [message #781181 is a reply to message #781007] Fri, 20 January 2012 11:32 Go to previous messageGo to next message
Chris Delahunt is currently offline Chris Delahunt
Messages: 995
Registered: July 2009
Senior Member
I am not sure I have ever seen EclipseLink automatically add a hint other than when it is using rownum pagination on the Oracle platform. You can verify that EclipseLink isn't adding it to the SQL it issues by turning logging on using <property name="eclipselink.logging.level" value="FINEST"/>. If you are issuing native queries (named or otherwise) EclipseLink will not modify the sql in anyway, so I don't see how the NOEXPAND hint gets added in one case but not another - you may need to check the driver and database settings. This is more likely since EclipseLink cannot tell that you are using a view vs a database table, and so wouldn't know to use the hint, but the database might.

Best Regards,
Chris
Re: NOEXPAND hints and bind-parameters [message #781182 is a reply to message #781007] Fri, 20 January 2012 11:44 Go to previous message
Chris Delahunt is currently offline Chris Delahunt
Messages: 995
Registered: July 2009
Senior Member
Using google I http://dba.stackexchange.com/questions/3044/noexpand-hint-for-non-enterpise-edition-and-performance
" In SQL Server Enterprise, the query optimizer automatically considers the indexed view. To use an indexed view in all other editions, the NOEXPAND table hint must be used." It could be you are using SQL Server Enterprise which decided to use an indexed view for some of your queries, making it appear to have the NOEXPAND hint so that it can use the indexed view.

Best of luck,
Chris
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