"Memory leak" in SqlEventListener

We’re experiencing memory growth issues when using the SqlClientDiagnosticSubscriber. Took a dump of the running process and analyzed it in dotMemory. Turns out a lot memory is allocated by _processingSpans.

When looking at the code I see that “ended” spans are never removed from the dictionary. Perhaps there is a good reason to leave the span in the dictionary after it has ended. I don’t know. But if there isn’t, and the span should be removed from the dictionary, then a quick fix would be to replace if (!_processingSpans.TryGetValue(id, out var item)) with if (!_processingSpans.TryRemove(id, out var item))

private void ProcessEndExecute(IReadOnlyList<object> payload)
{
	if (payload.Count != 3)
	{
		_logger?.Debug()
			?.Log("EndExecute event has {PayloadCount} payload items instead of 3. Event processing is skipped.", payload.Count);
		return;
	}

	var id = Convert.ToInt32(payload[0]);
	var compositeState = Convert.ToInt32(payload[1]);
	var sqlExceptionNumber = Convert.ToInt32(payload[2]);
	var stop = Stopwatch.GetTimestamp();

	_logger?.Trace()
		?.Log("Process EndExecute event. Id: {Id}. Composite state: {CompositeState}. Sql exception number: {SqlExceptionNumber}.", id,
			compositeState, sqlExceptionNumber);

	if (!_processingSpans.TryGetValue(id, out var item))
	{
		_logger?.Warning()
			?.Log("Failed capturing sql statement (failed to remove from ProcessingSpans).");
		return;
	}

	var isSuccess = (compositeState & 1) == 1;
	var isSqlException = (compositeState & 2) == 2;
	// 4 - is synchronous

	item.Span.Duration = ((stop - item.Start) / (double)Stopwatch.Frequency) * 1000;

	if (isSqlException)
	{
		item.Span.CaptureError("Exception has occurred", sqlExceptionNumber != 0 ? $"SQL Exception {sqlExceptionNumber}" : null,
			null);
	}

	item.Span.End();
}

[nilsgstrabo]

Can confirm that 1.5.1 fixes the memory issue @gregkalapos Tested 1.5.0 and 1.5.1 with the same requests, and as you can see the spans are successfully removed from the dictionary (as expected).

With version 1.5.0

With version 1.5.1

[nilsgstrabo]

Thank you @gregkalapos! I will test tomorrow and let you know. Really appreciate your quick response!