In certain circumstances one may find that the event forwarding queue is backed up or growing excessivelytable, also you can see the table EVENT_SYNC_BUFFER growing fastly.
Normally, we use the tool "opr-event-sync" to cancel the forwarding events in the queue. but sometimes, the command may fail or takes very long time to cancel the events from the queue. in such situation, to recover the system asap, we can clear most old events from database directly by:
Delete * from [dbo].[EVENT_SYNC_BUFFER] where time_created < '2018-03-21'
(it will remove the events created before Mar. 21st, 2018)