Infrastructure

The replication task queue implemented in Hazelcast uses postgres as a backing store to preserve state between restarts.

Observing event log messages and correlating with code where those events are emitted, it appears that tasks are not being deleted from the backing store.

```
ReplicationManager

removeReplicationTasksForPid(); log message = "removing replication tasks for pid: ..."
ReplicationTaskRepository taskRepository.delete(tasks)

```

Sequence of log messages for a single PID, starting with `removeReplicationTasksForPid()`:

```
[ INFO] 2018-07-04 13:19:21,996 [pool-6-thread-1] (ReplicationManager:removeReplicationTasksForPid:779) removing replication tasks for pid: ess-dive-112ed52c7689908-20180328T192607490

[ INFO] 2018-07-04 13:19:22,095 [pool-6-thread-1] (ReplicationManager:createAndQueueTasks:390) Added 0 MNReplicationTasks to the queue for ess-dive-112ed52c7689908-20180328T192607490

[ WARN] 2018-07-04 13:19:22,096 [pool-6-thread-1] (ReplicationManager:requeueReplicationTask:794) In Replication Manager, task that should exist 'in process' does not exist. Creating new task for pid: ess-dive-112ed52c7689908-20180328T192607490
```

`ReplicationTaskRepository` is an interface that extends `org.springframework.data.repository.PagingAndSortingRepository`. An instance is created by `repositoryFactory.getReplicationTaskRepository()` using the `ReplicationRepositoryFactory` passed to the `ReplicationManager` constructor.

The implementation of `ReplicationRepositoryFactory` is `ReplicationPostgresRepositoryFactory`