There are several spots during the Buffered LogMiner change event source where the number of buffered events is calculated unnecessary.

1. When a START event is observed, no change in buffered events.
2. When an event is not enqueued, thus no change in buffered events.
3. When a COMMIT event is observed, where transaction has 0 events.

With (1) and (2), this can lead to a possible performance drop where we may get a large number of start/commit transaction markers for transactions that have no events of interest in the processing loop. In these two situations, the update is necessary.

For (2), when events are enqueued, we only need to adjust this if the event is actually enqueued. Right now the counter is adjusted for each enqueue call, which can be costly where we re-read/mine events.