/// <summary>
/// This message is sent from NEventstore after a commit is created. Commits might not be sent in the correct order however...
/// </summary>
/// <param name="msg"></param>
private void Received(CommitNotification msg)
{
_cache.Cache(msg.Commit);
_backlogCommitCount++;
if (!_currentCheckpoint.HasValue)
{
HandleFirstCommitAfterStartup(msg);
}
else
{
List <OrderedCommitNotification> cachedCommits = _cache.GetCommitsAfter(_currentCheckpoint.Get());
if (cachedCommits.Count > 0)
{
//local cache can ensure we have all the commits in order: project them
cachedCommits.ForEach(SendCommitToProjectors);
_backlogCommitCount = 0;
}
else
{
//local cache can't ensure we have all the commits in order
PollEventStoreWithExponentialBackoff(msg, _currentCheckpoint);
}
}
}
/// <summary>
/// The first commit we recieve can't be ordered by this actor.
/// </summary>
/// <param name="msg"></param>
private void HandleFirstCommitAfterStartup(CommitNotification msg)
{
//NEventStore doesn't allow the getting of a commit prior to a checkpoint. so we cant' create the ordered commit notification, instead we just treat this commit as the head
_currentCheckpoint = msg.Commit.CheckpointToken.ToSome(); //this commit is now considered the head
//but tell the projectors to catchup, otherwise 1st commit is not projected
Context.ActorSelection(_projectorsBroadCastRouter).Tell(new CatchUpMessage()); //tell projectors to catch up
}
private void PollEventStoreWithExponentialBackoff(CommitNotification msg, Option <long> afterCheckpoint)
{
//we poll exponentially, on the size of the backlog of unprojected commits
if (!IsPowerOfTwo((ulong)_backlogCommitCount))
{
return;
}
//log @warning. Detected situation is entirely normal and expected, but should be rare.
var currentCheckpoint = _currentCheckpoint.Map(x => x.ToString()).GetOrElse("no currentcommit");
Context.GetLogger()
.Warning(
"Received a commit notification (checkpoint {0}) whilst currentcheckpoint={1}. Commit couldn't be serialised via the cache so polling with @backlog count={2}",
msg.Commit.CheckpointToken, currentCheckpoint, _backlogCommitCount);
var eventStorePollerActor = MakeNewEventStorePollerActor();
//ask the poller to get the commits directly from the store
Context.ActorSelection(eventStorePollerActor.Path)
.Tell(new SendCommitAfterCurrentHeadCheckpointMessage(afterCheckpoint, _backlogCommitCount.ToSome()));
}
