Gerrit: Internal Server Error with java.sql.SQLRecoverableException: Closed Connection - database

Question

From time to time we get Internal Server errors when we push to Gerrit. In the logs we see that the connection the connection is closed before the transaction is completed. (See log below)
We're using an Oracle DB with the following settings:
[database]
type = ORACLE
poolmaxidle = 16
database = db/ReviewDB
port = 1521
instance = infrapd1
hostname = HOSTNAME
connectionpool = true
username = USERNAME
poollimit = 32
dataSourceInterceptorClass = com.googlesource.gerrit.plugins.javamelody.MonitoringDataSourceInterceptor
In the logs we see errors like these when we get an Internal Server error:
[2015-02-13 15:49:51,505] ERROR com.google.gerrit.server.git.ReceiveCommits : Can't insert change/patchset for PROJECT
com.google.gerrit.server.git.InsertException: Error inserting change/patchset
at com.google.gerrit.server.git.ReceiveCommits$1.apply(ReceiveCommits.java:258)
at com.google.gerrit.server.git.ReceiveCommits$1.apply(ReceiveCommits.java:249)
at com.google.common.util.concurrent.Futures$MappingCheckedFuture.mapException(Futures.java:1672)
at com.google.common.util.concurrent.AbstractCheckedFuture.checkedGet(AbstractCheckedFuture.java:85)
at com.google.gerrit.server.git.ReceiveCommits.insertChangesAndPatchSets(ReceiveCommits.java:756)
at com.google.gerrit.server.git.ReceiveCommits.processCommands(ReceiveCommits.java:564)
at com.google.gerrit.server.git.AsyncReceiveCommits$Worker.run(AsyncReceiveCommits.java:90)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at com.google.gerrit.server.util.RequestScopePropagator$5.call(RequestScopePropagator.java:222)
at com.google.gerrit.server.util.RequestScopePropagator$4.call(RequestScopePropagator.java:201)
at com.google.gerrit.server.util.ThreadLocalRequestScopePropagator$1.call(ThreadLocalRequestScopePropagator.java:55)
at com.google.gerrit.server.util.RequestScopePropagator$1.call(RequestScopePropagator.java:98)
at com.google.gerrit.server.util.RequestScopePropagator$2.run(RequestScopePropagator.java:131)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:178)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:292)
at com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:364)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
Caused by: java.util.concurrent.ExecutionException: com.google.gwtorm.server.OrmException: Cannot set auto commit mode
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
at com.google.common.util.concurrent.ForwardingFuture.get(ForwardingFuture.java:63)
at com.google.common.util.concurrent.AbstractCheckedFuture.checkedGet(AbstractCheckedFuture.java:78)
... 17 more
Caused by: com.google.gwtorm.server.OrmException: Cannot set auto commit mode
at com.google.gwtorm.jdbc.JdbcSchema.rollback(JdbcSchema.java:80)
at com.google.gerrit.server.change.ChangeInserter.insert(ChangeInserter.java:177)
at com.google.gerrit.server.git.ReceiveCommits$CreateRequest.insertChange(ReceiveCommits.java:1585)
at com.google.gerrit.server.git.ReceiveCommits$CreateRequest.access$800(ReceiveCommits.java:1520)
at com.google.gerrit.server.git.ReceiveCommits$CreateRequest$1.call(ReceiveCommits.java:1551)
at com.google.gerrit.server.git.ReceiveCommits$CreateRequest$1.call(ReceiveCommits.java:1547)
at com.google.gerrit.server.util.RequestScopePropagator$1.call(RequestScopePropagator.java:96)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at com.google.common.util.concurrent.MoreExecutors$SameThreadExecutorService.execute(MoreExecutors.java:297)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:132)
at com.google.common.util.concurrent.AbstractListeningExecutorService.submit(AbstractListeningExecutorService.java:58)
at com.google.gerrit.server.git.ReceiveCommits$CreateRequest.insertChange(ReceiveCommits.java:1546)
at com.google.gerrit.server.git.ReceiveCommits.insertChangesAndPatchSets(ReceiveCommits.java:752)
... 16 more
Caused by: java.sql.SQLRecoverableException: Closed Connection
at oracle.jdbc.driver.PhysicalConnection.setAutoCommit(PhysicalConnection.java:3790)
at org.apache.commons.dbcp.DelegatingConnection.setAutoCommit(DelegatingConnection.java:371)
at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.setAutoCommit(PoolingDataSource.java:328)
at sun.reflect.GeneratedMethodAccessor69.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at net.bull.javamelody.JdbcWrapper$ConnectionInvocationHandler.invoke(JdbcWrapper.java:188)
at net.bull.javamelody.JdbcWrapper$DelegatingInvocationHandler.invoke(JdbcWrapper.java:285)
at com.sun.proxy.$Proxy17.setAutoCommit(Unknown Source)
at com.google.gwtorm.jdbc.JdbcSchema.rollback(JdbcSchema.java:78)
... 28 more
Any suggestions on how to resolve this? Any advise on how to improve the DB settings or debug the error? Any pointers are much appreciated.