[Hibernate-issues] [Hibernate-JIRA] Commented: (HB-587) Lazy collections not lazy when used with second level cache

[<leg...@at...>]

The following comment has been added to this issue:

     Author: Juho Snellman
    Created: Tue, 27 Jan 2004 3:35 PM
       Body:
The fix is working correctly on my tests (i.e. collection caching now improves performance, instead of the earlier dramatic performance loss). On one dataset, CVS Hibernate finishes in 3 minutes while 2.1.1 with the same cache configuration takes 46 minutes. 

Thanks!


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View the issue:

  http://opensource.atlassian.com/projects/hibernate/secure/ViewIssue.jspa?key=HB-587


Here is an overview of the issue:
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        Key: HB-587
    Summary: Lazy collections not lazy when used with second level cache
       Type: Bug

     Status: Closed
   Priority: Major
 Resolution: FIXED

 Original Estimate: Unknown
 Time Spent: Unknown
  Remaining: Unknown

    Project: Hibernate2
 Components: 
             core
   Fix Fors:
             2.1.2
   Versions:
             2.1.1

   Assignee: Gavin King
   Reporter: Juho Snellman

    Created: Tue, 30 Dec 2003 8:53 AM
    Updated: Tue, 27 Jan 2004 3:35 PM
Environment: Hibernate 2.1.1
ehcache

Description:
When an object is loaded from the second level cache, any of its collections that are found from the cache are immediately initialized.
This happens for both lazy and non-lazy collections. These initializations then cascade on to the contents of the collection, and their child-collections. 

For a sufficiently large and interconnected graph of objects this results in a disastrous performance loss when caching is enabled. In my particular case a test enabling caching increases the runtime of a test from about 12 minutes to over 40 minutes. In the latter case SessionImpl.getCachedCollection() takes up 68% of the runtime. Disabling caching only for collections brings the runtime back down.
 
Aside from the performance issue, it seems to me that initializing lazy collections is also conceptually wrong. Shouldn't laziness mean "no work is done unless it's neccessary", instead of "nothing is fetched from the DB unless it's neccessary"?

I'm pretty sure this didn't happen with Hibernate 2.0 and JCS. 


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