In case that connection is down then Sybase database throws SQL connection for preparing statement which causes that CommitMarkableResourceRecordRecoveryModule could ends in infinite loop.

I refer to the line of method delete(String jndiName, List<Xid> completedXids)
PreparedStatement prepareStatement = connection.prepareStatement(sql);
at
https://github.com/jbosstm/narayana/blob/4.17/ArjunaJTA/jta/classes/com/arjuna/ats/internal/jta/recovery/arjunacore/CommitMarkableResourceRecordRecoveryModule.java#L631

The test where I can hit this is:
We use mock XA resource and CMR JPA resource.
Test stops (halts) DB connection at commit phase on TestXAResource before commit was done on JPA CMR resource. This means that commit of JPA CMR resource fails. The recovery then tries to fix the troubles (in fact at the end there will be no fix as the in-doubt transaction is in heuristic state). During this fixing it tried to run sql query DELETE xid from CMR 'xids' table which ends in infinite loop.

The exception which floods the log is:
TRACE [com.arjuna.ats.jta] (Periodic Recovery) TransactionSynchronizationRegistryImple.getTransactionKey
TRACE [com.arjuna.ats.arjuna] (Periodic Recovery) Attempting to delete number of entries: 4
WARN  [com.arjuna.ats.arjuna] (Periodic Recovery) Could not handle the connection: java.sql.SQLException: JZ0C0: Connection is already closed.
 at com.sybase.jdbc4.jdbc.ErrorMessage.raiseError(ErrorMessage.java:765)
 at com.sybase.jdbc4.jdbc.SybConnection.checkConnection(SybConnection.java:3352)
 at com.sybase.jdbc4.jdbc.SybConnection.prepareStatement(SybConnection.java:1396)
 at com.sybase.jdbc4.jdbc.SybConnection.prepareStatement(SybConnection.java:1307)
 at com.sybase.jdbc4.jdbc.SybConnection.prepareStatement(SybConnection.java:1278)
 at com.sybase.jdbc4.jdbc.SybConnection.prepareStatement(SybConnection.java:2946)
 at org.jboss.jca.adapters.jdbc.BaseWrapperManagedConnection.doPrepareStatement(BaseWrapperManagedConnection.java:748)
 at org.jboss.jca.adapters.jdbc.BaseWrapperManagedConnection.prepareStatement(BaseWrapperManagedConnection.java:734)
 at org.jboss.jca.adapters.jdbc.WrappedConnection.prepareStatement(WrappedConnection.java:405)
 at com.arjuna.ats.internal.jta.recovery.arjunacore.CommitMarkableResourceRecordRecoveryModule.delete(CommitMarkableResourceRecordRecoveryModule.java:624) [jbossjts-jacorb-4.17.20.Final-redhat-1.jar:4.17.20.Final-redhat-1]
 at com.arjuna.ats.internal.jta.recovery.arjunacore.CommitMarkableResourceRecordRecoveryModule.periodicWorkFirstPass(CommitMarkableResourceRecordRecoveryModule.java:177) [jbossjts-jacorb-4.17.20.Final-redhat-1.jar:4.17.20.Final-redhat-1]
 at com.arjuna.ats.internal.arjuna.recovery.PeriodicRecovery.doWorkInternal(PeriodicRecovery.java:743) [jbossjts-jacorb-4.17.20.Final-redhat-1.jar:4.17.20.Final-redhat-1]
 at com.arjuna.ats.internal.arjuna.recovery.PeriodicRecovery.run(PeriodicRecovery.java:371) [jbossjts-jacorb-4.17.20.Final-redhat-1.jar:4.17.20.Final-redhat-1]