/// <summary> Catch up with locally stored data, without remote fetches. </summary>
/// <returns>
/// The number of events that have been passed to the projection.
/// </returns>
private uint CatchUpLocal()
{
var caughtUpWithProjection = false;
var eventsPassedToProjection = 0u;
while (true)
{
TEvent nextEvent;
try
{
// This might throw due to serialization error
// (but not for other reasons)
nextEvent = Stream.TryGetNext();
}
catch (Exception ex)
{
_log?.Warning($"[ES read] unreadable event at seq {Stream.Sequence}.", ex);
_projection.SetPossiblyInconsistent();
Quarantine.Add(Stream.Sequence, ex);
continue;
}
// No more local events left
if (nextEvent == null)
{
break;
}
var seq = Stream.Sequence;
if (_log != null && seq % 1000 == 0)
{
_log.Info($"[ES read] processing event at seq {seq}.");
}
if (caughtUpWithProjection || seq > _projection.Sequence)
{
caughtUpWithProjection = true;
try
{
++eventsPassedToProjection;
// This might throw due to event processing issues
// by one or more projection components
_projection.Apply(seq, nextEvent);
}
catch (Exception ex)
{
_log?.Warning($"[ES read] processing error on event at seq {seq}.", ex);
_projection.SetPossiblyInconsistent();
Quarantine.Add(seq, nextEvent, ex);
}
}
}
return(eventsPassedToProjection);
}
internal static async Task Catchup(
IReifiedProjection projection,
IEventStream stream,
CancellationToken cancel = default,
ILogAdapter log = null)
{
try
{
// Load project and discard events before that.
log?.Info("[ES init] loading projections.");
await projection.TryLoadAsync(cancel).ConfigureAwait(false);
var catchUp = projection.Sequence + 1;
log?.Info($"[ES init] advancing stream to seq {catchUp}.");
var streamSequence = await stream.DiscardUpTo(catchUp, cancel).ConfigureAwait(false);
if (cancel.IsCancellationRequested)
{
return;
}
if (streamSequence != projection.Sequence)
{
log?.Warning(
$"[ES init] projection seq {projection.Sequence} not found in stream (max seq is {streamSequence}: resetting everything.");
// Cache is apparently beyond the available sequence. Could happen in
// development environments with non-persistent events but persistent
// caches. Treat cache as invalid and start from the beginning.
stream.Reset();
projection.Reset();
}
}
catch (Exception e)
{
log?.Warning("[ES init] error while reading cache.", e);
// Something went wrong when reading the cache. Stop.
stream.Reset();
projection.Reset();
}
}
/// <summary>
/// Attempt to load this projection from the source, updating its
/// <see cref="Current"/> and <see cref="Sequence"/>.
/// </summary>
/// <remarks>
/// Object is unchanged if loading fails.
///
/// Obviously, as this object does not support multi-threaded access,
/// it should NOT be accessed in any way before the task has completed.
/// </remarks>
public async Task TryLoadAsync(CancellationToken cancel = default)
{
if (_cacheProvider == null)
{
_log?.Warning($"[{Name}] no read cache provider !");
return;
}
var sw = Stopwatch.StartNew();
IEnumerable <Task <CacheCandidate> > candidates;
try
{
candidates = await _cacheProvider.OpenReadAsync(Name);
}
catch (Exception ex)
{
_log?.Warning($"[{Name}] error when opening cache.", ex);
return;
}
foreach (var candidateTask in candidates)
{
CacheCandidate candidate;
try
{
candidate = await candidateTask;
}
catch (Exception ex)
{
_log?.Warning($"[{Name}] error when opening cache.", ex);
continue;
}
_log?.Info($"[{Name}] reading cache {candidate.Name}");
var stream = candidate.Contents;
try
{
// Load the sequence number from the input
uint seq;
using (var br = new BinaryReader(stream, Encoding.UTF8, true))
seq = br.ReadUInt32();
_log?.Debug($"[{Name}] cache is at seq {seq}.");
// Create a new stream to hide the write of the sequence numbers
// (at the top and the bottom of the stream).
var boundedStream = new BoundedStream(stream, stream.Length - 8);
// Load the state, which advances the stream
var state = await _projection.TryLoadAsync(boundedStream, cancel)
.ConfigureAwait(false);
if (state == null)
{
_log?.Warning($"[{Name}] projection could not parse cache {candidate.Name}");
continue;
}
// Sanity check: is the same sequence number found at the end ?
uint endseq;
using (var br = new BinaryReader(stream, Encoding.UTF8, true))
endseq = br.ReadUInt32();
if (endseq != seq)
{
_log?.Warning($"[{Name}] sanity-check seq is {endseq} in cache {candidate.Name}");
continue;
}
_log?.Info($"[{Name}] loaded {stream.Length} bytes in {sw.Elapsed:mm':'ss'.'fff} from cache {candidate.Name}");
Current = state;
Sequence = seq;
return;
// Do NOT set _possiblyInconsistent to false here !
// Inconsistency can have external causes, e.g. event read
// failure, that are not automagically solved by loading from cache.
}
catch (EndOfStreamException)
{
_log?.Warning($"[{Name}] incomplete cache {candidate.Name}");
// Incomplete streams are simply treated as missing
}
catch (Exception ex)
{
_log?.Warning($"[{Name}] could not parse cache {candidate.Name}", ex);
// If a cache file cannot be parsed, try the next one
}
finally
{
stream.Dispose();
}
}
}
public void Info(string message)
{
_log.Info(Elapsed + " " + message);
}
/// <inheritdoc/> public static void Info(object caller, object message, params object[] replacements) => _log.Info(caller, message, replacements);
/// <summary>
/// Attempt to load this projection from the source, updating its
/// <see cref="Current"/> and <see cref="Sequence"/>.
/// </summary>
/// <remarks>
/// Object is unchanged if loading fails.
///
/// Obviously, as this object does not support multi-threaded access,
/// it should NOT be accessed in any way before the task has completed.
/// </remarks>
public async Task TryLoadAsync(CancellationToken cancel = default(CancellationToken))
{
if (_cacheProvider == null)
{
_log?.Warning($"[{Name}] no read cache provider !");
return;
}
Stream source;
var sw = Stopwatch.StartNew();
try
{
source = await _cacheProvider.OpenReadAsync(Name);
}
catch (Exception ex)
{
_log?.Warning($"[{Name}] error when opening cache.", ex);
return;
}
if (source == null)
{
_log?.Info($"[{Name}] no cached data found.");
return;
}
try
{
// Load the sequence number from the input
uint seq;
using (var br = new BinaryReader(source, Encoding.UTF8, true))
seq = br.ReadUInt32();
_log?.Debug($"[{Name}] cache is at seq {seq}.");
// Load the state, which advances the stream
var state = await _projection.TryLoadAsync(source, cancel).ConfigureAwait(false);
if (state == null)
{
_log?.Warning($"[{Name}] projection could not parse cache.");
return;
}
// Sanity check: is the same sequence number found at the end ?
uint endseq;
using (var br = new BinaryReader(source, Encoding.UTF8, true))
endseq = br.ReadUInt32();
if (endseq != seq)
{
_log?.Warning($"[{Name}] sanity-check seq is {endseq}.");
return;
}
_log?.Info($"[{Name}] loaded from cache in {sw.Elapsed:mm':'ss'.'fff}.");
Current = state;
Sequence = seq;
// Do NOT set _possiblyInconsistent to false here !
// Inconsistency can have external causes, e.g. event read
// failure, that are not automagically solved by loading from cache.
}
catch (EndOfStreamException)
{
_log?.Warning($"[{Name}] cache is incomplete.");
// Incomplete streams are simply treated as missing
}
catch (Exception ex)
{
_log?.Warning($"[{Name}] could not parse cache.", ex);
throw;
}
}