public ChangeFeedReader(IConfiguration configuration, IHubContext <ClientHub> signalRHubContext)
{
var cosmosDbConfiguration = ChangeFeedReader.BuildConfigurationForSection(configuration, "CosmosDB");
this.cosmosDbConfiguration = cosmosDbConfiguration;
this.signalRHubContext = signalRHubContext;
TelemetryConfiguration telemetryConfiguration = TelemetryConfiguration.Active;
telemetryConfiguration.InstrumentationKey = ChangeFeedReader.DetectAppInsightsInstrumentationKey(configuration);
telemetryConfiguration.TelemetryInitializers.Add(new OperationCorrelationTelemetryInitializer());
telemetryConfiguration.TelemetryInitializers.Add(new HttpDependenciesParsingTelemetryInitializer());
this.telemetryClient = new TelemetryClient();
}
public Task StartAsync(CancellationToken cancellation)
{
if (this.isRunning)
{
return(Task.CompletedTask);
}
if (this.documentClient == null)
{
this.telemetryClient.TrackEvent($"Creating DocumentClient...");
this.documentClient = new DocumentClient(new Uri(this.cosmosDbConfiguration.Endpoint), this.cosmosDbConfiguration.MasterKey, ChangeFeedReader.BuildConnectionPolicy(this.cosmosDbConfiguration));
this.collectionLink = UriFactory.CreateDocumentCollectionUri(this.cosmosDbConfiguration.DatabaseName, this.cosmosDbConfiguration.CollectionName);
this.telemetryClient.TrackEvent($"DocumentClient ready.");
}
this.isRunning = true;
TimeSpan feedPollDelay = TimeSpan.FromMilliseconds(this.cosmosDbConfiguration.PollingInterval.HasValue ? this.cosmosDbConfiguration.PollingInterval.Value : ChangeFeedReader.DefaultPollingIntervalInMilliseconds);
return(Task.Run(async() =>
{
this.telemetryClient.TrackEvent($"ChangeFeedReader running.");
ChangeFeedOptions options = new ChangeFeedOptions
{
MaxItemCount = -1,
PartitionKeyRangeId = "0",
};
if (this.cosmosDbConfiguration.MaxItemCount.HasValue)
{
options.MaxItemCount = this.cosmosDbConfiguration.MaxItemCount.Value;
}
while (this.isRunning)
{
IDocumentQuery <Document> query = this.documentClient.CreateDocumentChangeFeedQuery(this.collectionLink, options);
do
{
ExceptionDispatchInfo exceptionDispatchInfo = null;
FeedResponse <Document> readChangesResponse = null;
var operation = this.telemetryClient.StartOperation(new RequestTelemetry()
{
Name = "ChangeFeedReader.ReadFeed"
});
DateTimeOffset feedDependencyStartTime = DateTimeOffset.UtcNow;
try
{
readChangesResponse = await query.ExecuteNextAsync <Document>();
this.telemetryClient.TrackMetric(new MetricTelemetry("CosmosDB.ChangeFeed.RU", readChangesResponse.RequestCharge));
this.telemetryClient.TrackDependency("CosmosDB.ChangeFeed", "ExecuteNextAsync", feedDependencyStartTime, DateTimeOffset.UtcNow.Subtract(feedDependencyStartTime), true);
options.RequestContinuation = readChangesResponse.ResponseContinuation;
}
catch (DocumentClientException ex)
{
exceptionDispatchInfo = ExceptionDispatchInfo.Capture(ex);
this.telemetryClient.TrackDependency("CosmosDB.ChangeFeed", "ExecuteNextAsync", feedDependencyStartTime, DateTimeOffset.UtcNow.Subtract(feedDependencyStartTime), false);
}
if (exceptionDispatchInfo != null)
{
DocumentClientException dcex = (DocumentClientException)exceptionDispatchInfo.SourceException;
if ((HttpStatusCode)dcex.StatusCode == HttpStatusCode.NotFound && (SubStatusCode)ChangeFeedReader.GetSubStatusCode(dcex) != SubStatusCode.ReadSessionNotAvailable)
{
// Most likely, the database or collection was removed while we were enumerating.
this.telemetryClient.TrackException(dcex);
this.telemetryClient.StopOperation(operation);
this.isRunning = false;
break;
}
else if ((HttpStatusCode)dcex.StatusCode == HttpStatusCode.Gone)
{
SubStatusCode subStatusCode = (SubStatusCode)ChangeFeedReader.GetSubStatusCode(dcex);
this.telemetryClient.TrackException(dcex);
}
else if ((int)dcex.StatusCode == 429 ||
(HttpStatusCode)dcex.StatusCode == HttpStatusCode.ServiceUnavailable)
{
this.telemetryClient.TrackEvent($"Retriable exception: {dcex.Message}");
}
else if (dcex.Message.Contains("Reduce page size and try again."))
{
this.telemetryClient.TrackEvent($"Page size error while reading the feed.");
// Temporary workaround to compare exception message, until server provides better way of handling this case.
if (!options.MaxItemCount.HasValue)
{
options.MaxItemCount = DefaultMaxItemCount;
}
else if (options.MaxItemCount <= 1)
{
this.telemetryClient.TrackEvent($"Cannot reduce maxItemCount further as it's already at {options.MaxItemCount}.");
this.telemetryClient.TrackException(new Exception("Cannot reduce maxItemCount"));
}
else
{
options.MaxItemCount /= 2;
this.telemetryClient.TrackEvent($"Reducing maxItemCount, new value: {options.MaxItemCount}.");
}
}
else
{
this.telemetryClient.TrackException(dcex);
}
if (dcex.RetryAfter != TimeSpan.Zero)
{
this.telemetryClient.TrackTrace($"Exception requires retryAfter, sleeping {dcex.RetryAfter.TotalMilliseconds} ms.");
await Task.Delay(dcex.RetryAfter, cancellation);
}
}
if (readChangesResponse != null)
{
var results = readChangesResponse.ToList();
if (results.Count > 0)
{
var lsn = results.First().GetPropertyValue <long>("_lsn");
this.telemetryClient.TrackTrace($"Detected {results.Count} documents. First _lsn {lsn}");
DateTimeOffset signalRDependencyStartTime = DateTimeOffset.UtcNow;
try
{
var response = results.Select((d) => new
{
items = d.GetPropertyValue <List <Pixel> >("items"),
_lsn = d.GetPropertyValue <long>("_lsn"),
});
await this.signalRHubContext.Clients.All.SendAsync("Changes", JsonConvert.SerializeObject(response));
this.telemetryClient.TrackDependency("SignalR", "SendAsync", signalRDependencyStartTime, DateTimeOffset.UtcNow.Subtract(signalRDependencyStartTime), true);
}
catch (Exception ex)
{
this.telemetryClient.TrackException(ex);
this.telemetryClient.TrackDependency("SignalR", "SendAsync", signalRDependencyStartTime, DateTimeOffset.UtcNow.Subtract(signalRDependencyStartTime), false);
}
this.telemetryClient.StopOperation(operation);
}
else
{
this.telemetryClient.TrackTrace($"No changes, sleeping {feedPollDelay.TotalMilliseconds} ms.");
this.telemetryClient.StopOperation(operation);
await Task.Delay(feedPollDelay, cancellation);
}
}
else
{
this.telemetryClient.StopOperation(operation);
}
}while (query.HasMoreResults && this.isRunning);
}
}));
}