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farrukh_najmi
 Post subject: EntityManager gracefully handle database restart?
PostPosted: Thu Dec 02, 2010 10:55 am 
Newbie

Joined: Thu Sep 14, 2006 12:08 pm
Posts: 19
In my servlet based webapp, I use the hibernate 3.5.0.Beta-1 EntityManager to access a postgres db. Sometimes the postgres db needs to be restarted. Whenever this happens the next query from my EntityManager fails like this:

Quote:
Caused by: org.hibernate.exception.JDBCConnectionException: could not execute query
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:97)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
at org.hibernate.loader.Loader.doList(Loader.java:2235)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2129)
at org.hibernate.loader.Loader.list(Loader.java:2124)
at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:411)
at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1083)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
at org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:93)
... 39 more
Caused by: org.postgresql.util.PSQLException: An I/O error occured while sending to the backend.
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:218)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:451)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:350)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:254)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1812)
at org.hibernate.loader.Loader.doQuery(Loader.java:697)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
at org.hibernate.loader.Loader.doList(Loader.java:2232)
... 47 more
Caused by: java.io.IOException: Stream closed
at sun.nio.cs.StreamEncoder.ensureOpen(StreamEncoder.java:26)
at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:121)
at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:212)
at org.postgresql.core.PGStream.flush(PGStream.java:507)
at org.postgresql.core.v3.QueryExecutorImpl.sendSync(QueryExecutorImpl.java:676)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:191)
... 55 more


What is the best practice for gracefully handling database restarts like this?
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farrukh_najmi
 Post subject: Re: EntityManager gracefully handle database restart?
PostPosted: Tue Dec 07, 2010 1:00 pm 
Newbie

Joined: Thu Sep 14, 2006 12:08 pm
Posts: 19
Hi Guys,

Does any one have any suggestions on my question. Please let me know if I was not clear in my post. Thanks.
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farrukh_najmi
 Post subject: Re: EntityManager gracefully handle database restart?
PostPosted: Wed Dec 08, 2010 6:19 pm 
Newbie

Joined: Thu Sep 14, 2006 12:08 pm
Posts: 19
farrukh_najmi wrote:
Hi Guys,

Does any one have any suggestions on my question. Please let me know if I was not clear in my post. Thanks.


I have tried adding logic to detect that PersistenceException is caused by a JDBCConnectionException and if so creating a new EntityManager to use for my query.
This does not seem to work either. The retried query using the new EntityManager gives the same PersistenceException is caused by a JDBCConnectionException. I have validated in debugger that the retry is done with a newly created EntityManager.

So my rephrased question is... How do I use force hibernate layer to create a new connection to the database if a newly created EntityManager does not do the trick? Where in hibernate layers is the connection to the database made?

I assume this is something many people before me have needed to do so please share your experience. Thanks.
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farrukh_najmi
 Post subject: [Solved] EntityManager gracefully handle database restart?
PostPosted: Wed Dec 08, 2010 6:59 pm 
Newbie

Joined: Thu Sep 14, 2006 12:08 pm
Posts: 19
I finally figured it out. To handle db restart gracefully I needed to recreate a new EntityManagerFactory and then use it to create new EntityManagers. Previously I was only creating new EntityManagers but the connection to db was cached somewhere in the EntityManagerFactory. HTH other folks. I must say I am surprised by the lack of help from the community. Was it because my question was so dumb and answer so obvious?
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