public async Task <TransactionBatch> NextAsync(CancellationToken token, TimeSpan waitPeriod)
{
var sw = new Stopwatch();
sw.Start();
TransactionBatch batch = null;
while (!_transactionBatchBuffer.TryTake(out batch) && sw.Elapsed <= waitPeriod && !token.IsCancellationRequested)
{
await Task.Delay(100);
}
return(batch);
}
private async Task PostBatch(CancellationToken token, BlockingCollection <TransactionBatch> transactionBatchBuffer, TransactionBatch transactionBatch)
{
// If the buffer is full then wait until capacity is available
// this ensures we have back pressure to prevent using up all our memory
bool added = false;
while (!added && !token.IsCancellationRequested)
{
if (transactionBatchBuffer.TryAdd(transactionBatch))
{
added = true;
}
else
{
await Task.Delay(100);
}
}
}
private async Task GroupTransactionsAsync(CancellationToken token,
List <TableSchema> tableSchemas,
Dictionary <string, BlockingCollection <ChangeRecord> > tableChangeBuffers,
BlockingCollection <TransactionBatch> transactionBatchBuffer,
int transactionBatchSizeLimit)
{
// create a "one item per table" buffer
var currentBuffer = new Dictionary <string, ChangeRecord>();
foreach (var tableSchema in tableSchemas)
{
currentBuffer.Add(tableSchema.TableName, null);
}
while (!token.IsCancellationRequested)
{
// Pull in next values of any table we don't have values for yet or any who previously signalled they had no data at that time
var keys = currentBuffer.Keys.ToList();
foreach (var tableKey in keys)
{
var bufferedValue = currentBuffer[tableKey];
if (bufferedValue == null || bufferedValue.LsnInt == NoDataAvailable)
{
ChangeRecord change = null;
if (tableChangeBuffers[tableKey].TryTake(out change))
{
currentBuffer[tableKey] = change;
}
}
}
if (currentBuffer.Values.All(x => x == null || x.LsnInt == NoDataAvailable))
{
await Task.Delay(1000);
continue;
}
// identify the lowest LSN currently available in our current buffer and a create a new batch for it
var currentTransaction = GetEarliestTransactionId(currentBuffer);
var transactionBatch = new TransactionBatch();
transactionBatch.Id = currentTransaction;
transactionBatch.Part = 1;
// Pull data from all table buffers for this LSN
var matchingTables = GetTablesOfTransaction(currentBuffer, currentTransaction.LsnInt);
foreach (var tableName in matchingTables)
{
// add the first change of the transaction from our current buffer
transactionBatch.Changes.Add(currentBuffer[tableName]);
// keep consuming from this table buffer until either the LSN does not match our current LSN
// or the table reader signals that we have reached the end of the buffer and no more items will arrive
var tableBuffer = tableChangeBuffers[tableName];
bool consume = true;
while (consume && !tableBuffer.IsAddingCompleted)
{
ChangeRecord next = null;
if (tableChangeBuffers[tableName].TryTake(out next))
{
if (next.LsnInt == currentTransaction.LsnInt)
{
transactionBatch.Changes.Add(next);
// if we have reached the maximum batch size the post and and create another
if (transactionBatch.Changes.Count > transactionBatchSizeLimit)
{
await PostBatch(token, transactionBatchBuffer, transactionBatch);
var nextPart = new TransactionBatch();
nextPart.Part = transactionBatch.Part + 1;
nextPart.Id = transactionBatch.Id;
nextPart.IsMultiPart = true;
transactionBatch = nextPart;
}
}
else
{
// store the value in our current buffer for a future transaction batch
currentBuffer[tableName] = next;
consume = false;
}
}
else
{
// there is no data in the buffer but the buffer is not completed. This means that the table reader is slower than us. Wait a little.
await Task.Delay(100);
}
}
}
// all data has been pulled from the buffers for this transaction
// now we post it to the TransactionBatch buffer.
await PostBatch(token, transactionBatchBuffer, transactionBatch);
}
}
