public async Task <ChangeBatch> GetChangeBatchAsync(TableSchema tableSchema, byte[] fromLsn, byte[] fromSeqVal, byte[] toLsn, int batchSize)
{
return(await _cdcRepository.GetChangeBatchAsync(tableSchema, fromLsn, fromSeqVal, toLsn, batchSize));
}
private async Task ReadTransactionsAsync(CancellationToken token, TableSchema tableSchema, int batchSize, BlockingCollection <ChangeRecord> changes, byte[] lastProcessedLsn)
{
byte[] toLsn = await _cdcRepository.GetMaxLsnAsync();
byte[] fromLsn = await GetInitialFromLsnAsync(tableSchema, lastProcessedLsn);
try
{
byte[] fromSeqVal = null;
bool waitingForChanges = false;
// outer loop sets the upper LSN range, inner loop iteratively reads up to that LSN
while (!token.IsCancellationRequested)
{
bool unfinishedLsn = false;
bool moreOfCurrentRange = true;
while (moreOfCurrentRange && !token.IsCancellationRequested)
{
// once we've caught up with the current target LSN, we'll exit the inner loop and go get the latest upper LSN
if (GetBigInteger(fromLsn) <= GetBigInteger(toLsn))
{
ChangeBatch batch = null;
if (unfinishedLsn)
{
batch = await _cdcRepository.GetChangeBatchAsync(tableSchema, fromLsn, fromSeqVal, toLsn, batchSize);
}
else
{
batch = await _cdcRepository.GetChangeBatchAsync(tableSchema, fromLsn, toLsn, batchSize);
}
if (batch.Changes.Any())
{
waitingForChanges = false;
//Console.WriteLine($"Table {tableName} - Retrieved block #{blockCounter} with {batch.Changes.Count} changes");
var enumerator = batch.Changes.GetEnumerator();
if (!enumerator.MoveNext())
{
break;
}
while (!token.IsCancellationRequested)
{
if (changes.TryAdd(enumerator.Current, 1000))
{
if (!enumerator.MoveNext())
{
break;
}
}
}
fromLsn = batch.Changes.Last().Lsn;
fromSeqVal = batch.Changes.Last().SeqVal;
moreOfCurrentRange = batch.MoreChanges;
unfinishedLsn = batch.MoreOfLastTransaction;
if (unfinishedLsn)
{
fromSeqVal = Increment(fromSeqVal);
}
else
{
fromLsn = Increment(fromLsn);
}
}
else
{
moreOfCurrentRange = false;
unfinishedLsn = false;
//Console.WriteLine($"Table {tableName} - No changes");
}
}
else
{
moreOfCurrentRange = false;
unfinishedLsn = false;
//Console.WriteLine($"Table {tableName} - No changes");
}
}
var latestLsn = await _cdcRepository.GetMaxLsnAsync();
if (latestLsn.SequenceEqual(toLsn))
{
if (!waitingForChanges)
{
// add a change record that signals to the Transaction Grouping Task that there are no new changes available
// this is important as the Transaction Grouping Task needs to differentiate between a slow reader and no data
var noDataSignalRecord = GetNoDataSignalRecord(tableSchema);
changes.TryAdd(noDataSignalRecord, 5000);
}
waitingForChanges = true;
// blocks until a new upper LSN is available
// note that a new upper LSN is published every five minutes by SQL Server even when no changes have occurred
toLsn = await GetLatestUpperLsnAsync(token, toLsn);
}
else
{
toLsn = latestLsn;
}
}
}
catch (Exception ex)
{
throw new ReaderException("Reader failure", ex, fromLsn);
}
}