MemoryLeak: Hibernate Sessions

[fviale]

Analyse of a heap dump shows a large heap memory usage due to hibernate session factory and QueryPlanCache from SchedulerDBManager

Class Name                                                                                       | Shallow Heap | Retained Heap
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org.hibernate.internal.SessionFactoryImpl @ 0x6db944410                                          |          136 |   445 322 392
|- <class> class org.hibernate.internal.SessionFactoryImpl @ 0x6db955028                         |           16 |            96
|- dialect org.hibernate.dialect.HSQLDialect @ 0x6db944358                                       |           72 |         6 040
|- serviceRegistry org.hibernate.service.internal.SessionFactoryServiceRegistryImpl @ 0x6db9443b0|           48 |        11 032
|- properties java.util.Properties @ 0x6db9443e0                                                 |           48 |         3 616
|- sessionFactoryOptions org.hibernate.boot.internal.SessionFactoryOptionsImpl @ 0x6db944498     |          160 |           536
|- jdbcServices org.hibernate.engine.jdbc.internal.JdbcServicesImpl @ 0x6db9a90b0                |           32 |            64
|- uuid java.lang.String @ 0x6db9a9cd8  e278da6b-637c-4fbe-b870-6b1868b68398                     |           24 |           112
|- cacheAccessStrategiesMap java.util.HashMap @ 0x6db9d9fb8                                      |           48 |            48
|- typeHelper org.hibernate.internal.TypeLocatorImpl @ 0x6db9d9fe8                               |           16 |            16
|- typeResolver org.hibernate.type.TypeResolver @ 0x6db9d9ff8                                    |           24 |         6 280
|- queryPlanCache org.hibernate.engine.query.spi.QueryPlanCache @ 0x6db9daaa0                    |           32 |   443 339 416
|- entityNameResolvers java.util.concurrent.ConcurrentHashMap @ 0x6db9dde50                      |           64 |            88
|- observer org.hibernate.internal.SessionFactoryObserverChain @ 0x6db9dde90                     |           16 |           200
|- namedQueryRepository org.hibernate.internal.NamedQueryRepository @ 0x6db9dfe60                |           32 |        16 264
|- collectionRolesByEntityParticipant java.util.Collections$UnmodifiableMap @ 0x6db9dff50        |           32 |         1 616
|- collectionMetadata java.util.Collections$UnmodifiableMap @ 0x6db9dff70                        |           32 |           416
|- collectionPersisters java.util.HashMap @ 0x6db9dffb0                                          |           48 |           400
|- cacheAccess org.hibernate.internal.CacheImpl @ 0x6db9e26e0                                    |           40 |           104
|- sqlFunctionRegistry org.hibernate.dialect.function.SQLFunctionRegistry @ 0x6db9e4df8          |           16 |         3 104
|- filters java.util.HashMap @ 0x6db9e5928                                                       |           48 |            48
|- identifierGenerators java.util.HashMap @ 0x6db9e5998                                          |           48 |           448
|- classMetadata java.util.Collections$UnmodifiableMap @ 0x6db9e5b58                             |           32 |           512
|- entityPersisters java.util.HashMap @ 0x6db9e5b78                                              |           48 |           464
|- settings org.hibernate.cfg.Settings @ 0x6db9ea160                                             |           24 |            24
|- imports java.util.HashMap @ 0x6db9ea2e8                                                       |           48 |         1 536
'- Total: 25 of 27 entries; 2 more                                                               |              |              
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The session factory maintains a cache of compiled queries. If this cache is not cleaned up, it keeps growing over time

A discussion maybe/maybenot linked:
https://stackoverflow.com/questions/17823599/possible-memory-leak-due-to-org-hibernate-internal-sessionfactoryimpl

A discussion most likely linked:
https://stackoverflow.com/questions/31557076/spring-hibernate-query-plan-cache-memory-usage

[yinan-liu]

if we instantiate a session factory once and only once (e.g. SchedulerDBManager is a singleton), it is ok, we use factory to create the session and close the session when it is finish. If we keep creating factory or never close the session, than we will have problem

[fviale]

Indeed the problem does not seem to come from Session, but from QueryPlanCache.

This suggestion from the attached thread seems to be pertinent:

Try adding the new properties hibernate.query.plan_cache_max_size and hibernate.query.plan_parameter_metadata_max_size

It seems to work for now, if I set those parameters very low (16 and 128)