Calling synchronous flush means sending all events in the buffer to the work queue and waiting for them to be processed. But if you are using the on_failure callback to resend failed events, those failed events will be placed back in the buffer and won't block the synchronous flush from finishing. Presumably if you are using the synchronous flush then you want to wait for retries to complete as well.
Calling synchronous flush means sending all events in the buffer to the work queue and waiting for them to be processed. But if you are using the on_failure callback to resend failed events, those failed events will be placed back in the buffer and won't block the synchronous flush from finishing. Presumably if you are using the synchronous flush then you want to wait for retries to complete as well.