Low during the UpgradeTask1825 it is very likely that hibernate's id generator will have to access db to reset the id boundaries. When doing that it requires a new connection and because the connection pool would be used up by upgrade threads it will wait forever to acquire a connection (since the threads will not give one up until they finish and they cannot finish because they also access synchronized id generation method).
UpgradeTask:pool-4-thread-7 [WAITING] CPU time: 0:00 java.lang.Object.wait(long) com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(long) com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(long) com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(long) com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection() com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection() net.sf.hibernate.connection.C3P0ConnectionProvider.getConnection() net.sf.hibernate.impl.BatcherImpl.openConnection() net.sf.hibernate.id.TableGenerator.generate(SessionImplementor, Object) com.atlassian.hibernate.ResettableTableHiLoGenerator.generate(SessionImplementor, Object) .... UpgradeTask:pool-4-thread-6 [BLOCKED] CPU time: 0:00 com.atlassian.hibernate.ResettableTableHiLoGenerator.generate(SessionImplementor, Object) net.sf.hibernate.impl.SessionImpl.saveWithGeneratedIdentifier(Object, Cascades$CascadingAction, Object) net.sf.hibernate.impl.SessionImpl.save(Object) net.sf.hibernate.impl.SessionImpl.saveOrUpdate(Object) org.springframework.orm.hibernate.HibernateTemplate$12.doInHibernate(Session)
