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cneuwirt
 Post subject: Possible Memory Leak with SqlString
PostPosted: Wed Feb 08, 2006 8:11 am 
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Joined: Tue May 31, 2005 9:55 am
Posts: 67
Need help with Hibernate? Read this first:
http://www.hibernate.org/ForumMailingli ... AskForHelp

Hibernate version:

1.0.1.0

Name and version of the database you are using:

MS Sql Server 2000


I deployed an application that makes heavy use of dynamic HQL Query String and their execution. I noticed the application was growing in memory quite rapdily so I ran a memory profiler on it. The profiler showed that the SqlString instance count was growing uncontrollably. Does NHibernate try and cache these HQL statements?

Should I create a JIRA issue for this?

thanks,
craig
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sergey
 Post subject:
PostPosted: Wed Feb 08, 2006 9:46 am 
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Joined: Wed May 11, 2005 4:59 pm
Posts: 1766
Location: Prague, Czech Republic
Yes, please create a JIRA issue. An example exhibiting the problem would be nice.
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pandrija
 Post subject: SqlString
PostPosted: Thu Mar 09, 2006 10:15 am 
Newbie

Joined: Thu Mar 09, 2006 10:09 am
Posts: 5
Hello,

I'm having the same problem. We didn't notice it until we started doing load tests, and now we're running out of time with the project deadline. I look in JIRA but I cannot see that this bug was reported.
We're using the same NHibernate version/database configuration.
Please help!

Peter.
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pandrija
 Post subject:
PostPosted: Fri Mar 10, 2006 5:27 am 
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Joined: Thu Mar 09, 2006 10:09 am
Posts: 5
I was a problem on our side after all...
Some of us were using Query API with query strings created via concatenation, instead of using parameters, so the number of cached queries was growing uncontrollably.

regards,
P.
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cneuwirt
 Post subject:
PostPosted: Tue Mar 21, 2006 3:58 pm 
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Joined: Tue May 31, 2005 9:55 am
Posts: 67
Sorry for the late reply.

I created the issue for this

http://jira.nhibernate.org/browse/NH-559


I am also creating query strings through concatention and not using parameters. Is there a way to limit the number of cached queries?

thanks,
craig
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pandrija
 Post subject:
PostPosted: Tue Mar 21, 2006 4:34 pm 
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Joined: Thu Mar 09, 2006 10:09 am
Posts: 5
Hi,

I wouldn't say this is a bug. Basically, you should use ISession.Find() function if you don't want to use paramertised queries. Query caching should be OK, beacuse in normal Query use (without concatenation) total number of unique queries in one application shouldn't grow unlimitedly.

P.
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cneuwirt
 Post subject:
PostPosted: Tue Mar 21, 2006 10:42 pm 
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Joined: Tue May 31, 2005 9:55 am
Posts: 67
I agree with you that the number of queries is usually limited?

Does ISession.Find() cache the queries too? I use ISession.CreateQuery so I can set SetFirstResult and SetMaxResults?

thanks,
craig
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cneuwirt
 Post subject:
PostPosted: Wed Mar 22, 2006 9:35 am 
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Joined: Tue May 31, 2005 9:55 am
Posts: 67
After doing some tests, it appears that ISession.Find suffers from the same memory consumpltion problem. Is using parameterized queries the only way to prevent this memory consumption?

thanks,
craig
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pandrija
 Post subject:
PostPosted: Wed Mar 22, 2006 9:40 am 
Newbie

Joined: Thu Mar 09, 2006 10:09 am
Posts: 5
Hi,

We had no more memory leaks after we changed the code to use Find().

P.
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cneuwirt
 Post subject:
PostPosted: Wed Mar 22, 2006 10:26 am 
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Joined: Tue May 31, 2005 9:55 am
Posts: 67
Even when using concatentated queries? Hmm, I wrote a simple unit test that performed 1000 Session.Find with different queries. I used GC.GetTotalMemory to get the bytes before and after the queries and it seemd to suggest significat memory consumption. I made sure I did a GC.Collect before getting the results.

My problem with parameterized queries is that I want to use the IN clause with a composite identifier and I don't think that is supported.

craig
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pandrija
 Post subject:
PostPosted: Wed Mar 22, 2006 10:29 am 
Newbie

Joined: Thu Mar 09, 2006 10:09 am
Posts: 5
You closed the session, I guess?
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cneuwirt
 Post subject:
PostPosted: Wed Mar 22, 2006 10:47 am 
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Joined: Tue May 31, 2005 9:55 am
Posts: 67
I sure did.

Code:
GC.Collect();

Simple simple = CreateAndSaveSimple();
   
long bytesBefore = GC.GetTotalMemory(true);

for (int i = 0; i < 1000; ++i)
{
   using( ISession s1 = OpenSession() )
   {
      IList results = s1.Find("select s from Simple s where s.id = " + i);

      GC.Collect();

      long bytesAfter = GC.GetTotalMemory(true);
      long memoryUsed = bytesAfter - bytesBefore;

      Assert.IsTrue(memoryUsed <= 30000, "Memory used was " + memoryUsed + " bytes");   
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cneuwirt
 Post subject:
PostPosted: Wed Mar 22, 2006 11:24 am 
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Joined: Tue May 31, 2005 9:55 am
Posts: 67
sergey,

Is it true that ISession.Find and ISession.CreateQuery will accumulate the distinct query string idefinitely?

thanks,
craig
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