/// <summary>
/// Does a stream already exist for this event stream identity
/// </summary>
/// <remarks>
/// We use the existence of the stream footer record as proof of stream existence
/// </remarks>
protected async internal Task <bool> StreamAlreadyExists()
{
TableEntityKeyRecord streamFooter = null;
TableOperation getKeyRecord = TableOperation.Retrieve <TableEntityKeyRecord>(this.InstanceKey, SequenceNumberAsString(0));
await Table.CreateIfNotExistsAsync();
TableResult getFooter = await Table.ExecuteAsync(
getKeyRecord);
if (getFooter != null)
{
if (getFooter.Result != null)
{
streamFooter = (TableEntityKeyRecord)getFooter.Result;
}
}
if (null != streamFooter)
{
return(true);
}
return(false);
}
/// <summary>
/// Does a stream already exist for this event stream identity
/// </summary>
/// <remarks>
/// We use the existence of the stream footer record as proof of stream existence
/// </remarks>
protected internal bool StreamAlreadyExists()
{
TableEntityKeyRecord streamFooter = null;
streamFooter = (TableEntityKeyRecord)Table.Execute(
TableOperation.Retrieve <TableEntityKeyRecord>(this.InstanceKey, SequenceNumberAsString(0)),
requestOptions: null,
operationContext: GetDefaultOperationContext()).Result;
if (null != streamFooter)
{
return(true);
}
return(false);
}
/// <summary>
/// Increment the sequence number for this event stream and return the new number
/// </summary>
/// <remarks>
/// This is done before the event itself is written so that a partial failure leaves a gap in the event stream which is
/// less harmful than an overwritten event record
/// </remarks>
private async Task <int> IncrementSequenceNumber()
{
bool recordUpdated = false;
int tries = 0;
TableEntityKeyRecord streamFooter = null;
while (!recordUpdated)
{
tries += 1;
// read in the a [TableEntityKeyRecord]
streamFooter = (TableEntityKeyRecord)Table.Execute(
TableOperation.Retrieve <TableEntityKeyRecord>(this.InstanceKey, SequenceNumberAsString(0)),
operationContext: GetDefaultOperationContext()).Result;
if (null == streamFooter)
{
streamFooter = new TableEntityKeyRecord(this);
}
streamFooter.LastSequence += 1;
try
{
TableResult tres = null;
if (string.IsNullOrWhiteSpace(streamFooter.ETag))
{
tres = await Table.ExecuteAsync(TableOperation.Insert(streamFooter));
}
else
{
tres = await Table.ExecuteAsync(TableOperation.Replace(streamFooter));
}
if (tres.HttpStatusCode == 204)
{
recordUpdated = true;
}
}
catch (Microsoft.Azure.Cosmos.Table.StorageException sEx)
{
if (sEx.RequestInformation.HttpStatusCode == (int)HttpStatusCode.PreconditionFailed)
{
// Precondition Failed - could not update the footer due to a concurrency error
recordUpdated = false;
// Wait a random-ish amount of time
int delayMilliseconds = 13 * new Random().Next(10, 100);
await Task.Delay(delayMilliseconds);
}
else
{
throw new EventStreamWriteException(this, streamFooter.LastSequence,
message: "Unable to increment the stream sequence number due to storage error",
source: "Table Event Stream Writer",
innerException: sEx);
}
}
if (tries > 500)
{
// catastrophic deadlock
throw new EventStreamWriteException(this, streamFooter.LastSequence,
message: "Unable to increment the stream sequence number due to deadlock",
source: "Table Event Stream Writer");
}
}
if (null != streamFooter)
{
if (streamFooter.Deleting)
{
// Do not allow a write to an event stream that is being deleted
throw new EventStreamWriteException(this,
streamFooter.LastSequence,
message: "Unable to write to this event stream as it is being deleted",
source: "Table Event Stream Writer");
}
return(streamFooter.LastSequence);
}
else
{
return(1);
}
}
/// <summary>
/// Delete all the records in the table linked to this event stream
/// </summary>
public async Task DeleteStream()
{
// 1- mark the stream footer as "Deleting"
bool recordUpdated = false;
int tries = 0;
TableEntityKeyRecord streamFooter = null;
while (!recordUpdated)
{
tries += 1;
// read in the a [TableEntityKeyRecord]
streamFooter = (TableEntityKeyRecord)Table.Execute(
TableOperation.Retrieve <TableEntityKeyRecord>(this.InstanceKey, SequenceNumberAsString(0)),
operationContext: GetDefaultOperationContext()).Result;
if (null == streamFooter)
{
streamFooter = new TableEntityKeyRecord(this);
}
streamFooter.Deleting = true;
string lastETag = streamFooter.ETag;
try
{
TableResult tres = await Table.ExecuteAsync(TableOperation.InsertOrReplace(streamFooter),
null,
new OperationContext
{
UserHeaders = new Dictionary <String, String>
{
{ "If-Match", lastETag }
}
});
if (tres.HttpStatusCode == 204)
{
recordUpdated = true;
}
}
catch (Microsoft.Azure.Cosmos.Table.StorageException sEx)
{
if (sEx.RequestInformation.HttpStatusCode == (int)HttpStatusCode.PreconditionFailed)
{
// Precondition Failed - could not update the footer due to a concurrency error
recordUpdated = false;
// Wait a random-ish amount of time
int delayMilliseconds = 13 * new Random().Next(10, 100);
System.Threading.Thread.Sleep(delayMilliseconds);
}
else
{
throw new EventStreamWriteException(this, streamFooter.LastSequence,
message: "Unable to set the Deleting flag stream sequence number due to storage error",
source: "Table Event Stream Writer",
innerException: sEx);
}
}
if (tries > 500)
{
// catastrophic deadlock
throw new EventStreamWriteException(this, streamFooter.LastSequence,
message: "Unable to set the Deleting flag number due to deadlock",
source: "Table Event Stream Writer");
}
}
// 2- delete the actual stream records in reverse order
if (Table != null)
{
// We need a continuation token as this is done in batches of 100...
TableContinuationToken token = new TableContinuationToken();
TableQuery getEventsToDeleteQuery = DeleteRowsQuery().Take(MAX_BATCH_SIZE);
do
{
var batches = new List <TableBatchOperation>();
int nextBatch = 0;
// create the query to be executed..
var segment = Table.ExecuteQuerySegmented(getEventsToDeleteQuery,
token,
operationContext: GetDefaultOperationContext());
// update the continuation token to get the next chunk of records
token = segment.ContinuationToken;
int currentRow = 0;
batches.Add(new TableBatchOperation());
foreach (DynamicTableEntity dteRow in segment)
{
if (currentRow % MAX_BATCH_SIZE == 0)
{
nextBatch += 1;
batches.Add(new TableBatchOperation());
}
batches[nextBatch].Add(TableOperation.Delete(dteRow));
currentRow += 1;
}
foreach (var batchExecute in batches)
{
if (batchExecute.Count > 0)
{
Table.ExecuteBatch(batchExecute);
}
}
} while (null != token);
}
}
