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NOEXPAND hints and bind-parameters [message #781041]

Thu, 19 January 2012 18:47

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?

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Re: NOEXPAND hints and bind-parameters [message #781131 is a reply to message #781041]

Fri, 20 January 2012 16:32

Chris Delahunt

Messages: 1266
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

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Re: NOEXPAND hints and bind-parameters [message #781135 is a reply to message #781041]

Fri, 20 January 2012 16:44

Chris Delahunt

Messages: 1266
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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Re: NOEXPAND hints and bind-parameters [message #781151 is a reply to message #781135]

Fri, 20 January 2012 18:03

Rich MacDonald

Messages: 18
Registered: December 2010

Junior Member

Chris, great suggestion. I had just seen that article myself and was arriving at the same idea at the same time Smile

I'd satisfied myself that eclipselink could not be adding the hint. There was a outside chance that the jdbc driver was, but that would be too weird. So I finally removed all my indexed views in sqlserver, and yes, the NOEXPAND hint went away.

Annoying that that sqlserver profiler and database tuner were reporting NOEXPAND in the queries. Dumb actually, because that should be "downstream" of where they are analyzing.

Oh well, at least I have made lateral progress. I used indexed views because I have expensive queries using Rank() and Max(), which are two procedures that sqlserver does not support inside indexed views. So I had created an indexed view for the "raw data" (the "inner portion" of the query), with appropriate indexes, then was using a normal view based on those indexes for the final/outer filtering. Unfortunately, with that configuration, the NOEXPAND causes braindead "full table scan" behavior.

Back to the drawing board ... but at least with a better idea. Thread closed and thanks for your help.

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Re: NOEXPAND hints and bind-parameters [message #781183 is a reply to message #781135]

Fri, 20 January 2012 18:03

Rich MacDonald

Messages: 18
Registered: December 2010

Junior Member

Chris, great suggestion. I had just seen that article myself and was arriving at the same idea at the same time :) I'd satisfied myself that eclipselink could not be adding the hint. There was a outside chance that the jdbc driver was, but that would be too weird. So I finally removed all my indexed views in sqlserver, and yes, the NOEXPAND hint went away.

Annoying that that sqlserver profiler and database tuner were reporting NOEXPAND in the queries. Dumb actually, because that should be "downstream" of where they are analyzing.

Oh well, at least I have made lateral progress. I used indexed views because I have expensive queries using Rank() and Max(), which are two procedures that sqlserver does not support inside indexed views. So I had created an indexed view for the "raw data" (the "inner portion" of the query), with appropriate indexes, then was using a normal view based on those indexes for the final/outer filtering. Unfortunately, with that configuration, the NOEXPAND causes braindead "full table scan" behavior.

Back to the drawing board ... but at least with a better idea. Thread closed and thanks for your help.

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