We are seeing Hibernate store a lot of information in the Session (first level cache) and eventually see OutOfMemory exceptions.

Solution Verified - Updated

Environment

  • JBoss Enterprise Application Platform (EAP)

    • 4
    • 5
    • 6
    • 7

  • Hibernate

    • 3.3.x
    • 5.3.x (bundled with JBoss EAP 7.4)

  • Heap analyzer shows for Hibernate 3.3:

      692,139,472 (32%) [88] 14 org/hibernate/engine/StatefulPersistenceContext 0x5ede0268
   659,080,192 (31%) [24] 3 org/hibernate/util/IdentityMap 0x5ede0678
   659,080,144 (31%) [32] 3 org/apache/commons/collections/SequencedHashMap 0x5ede0690
   24 (0%) [24] 1 array of java/util/Map$Entry 0x5ede0700
   96 (0%) [32] 22 class org/hibernate/util/IdentityMap 0x37fb9238
  27,924,656 (1%) [48] 2 java/util/HashMap 0x5ede02c0
   27,924,608 (1%) [994,528] 248,627 array of java/util/HashMap$Entry 0x87bc1c38
    640 (0%) [32] 4 java/util/HashMap$Entry 0x9a1a2708
    560 (0%) [32] 4 java/util/HashMap$Entry 0x9b0365e8
    560 (0%) [32] 4 java/util/HashMap$Entry 0xb19044c8

  • For Hibernate 5, in the dominator tree of Eclipse Memory Analyzer shows an instance of org.hibernate.engine.internal.StatefulPersistenceContext with a large retained heap:

      Class Name                                                           | Shallow Heap | Retained Heap | Percentage
  -----------------------------------------------------------------------------------------------------------------
  org.hibernate.engine.internal.StatefulPersistenceContext @ 0xce342030|          104 |   173,365,848 |     16.86%
  '- entitiesByKey java.util.HashMap @ 0xce342098                      |           48 |   173,364,592 |     16.86%
  -----------------------------------------------------------------------------------------------------------------

Issue

  • The application works fine for say 4 days at a stretch and then the JVM crashes with a OutofMemory error.
  • We see a lot of memory being used by org/hibernate/
  • We analyze this heap dump and we detect the high usage of org.hibernate.impl.SessionFactoryObjectFactory class (83% usage of memory).

Resolution

The session will grow this large when it has a very significant amount of objects living in it and can point to bad usage of the session. A few things that can lead to this are:

  • Batch processing without eviction/clear, see the hibernate docs on this
This would fall over with an `OutOfMemoryException` somewhere around the 50,000th row. That is because Hibernate caches all the newly inserted  
`Customer` instances in the session-level cache. In this chapter we will show you how to avoid this problem.
  • The session having a longer scope than is required
  • Doing queries without considering what they fetch

Regardless of the root cause the source is always loading many objects into the session without considering the implications.

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