The id functions as an opaque token for use when resuming an interrupted change stream.
Optional
clusterThe timestamp from the oplog entry associated with the event. For events that happened as part of a multi-document transaction, the associated change stream notifications will have the same clusterTime value, namely the time when the transaction was committed. On a sharded cluster, events that occur on different shards can have the same clusterTime but be associated with different transactions or even not be associated with any transaction. To identify events for a single transaction, you can use the combination of lsid and txnNumber in the change stream event document.
Optional
lsidThe identifier for the session associated with the transaction. Only present if the operation is part of a multi-document transaction.
The database dropped
Describes the type of operation represented in this change notification
Optional
splitWhen the change stream's backing aggregation pipeline contains the $changeStreamSplitLargeEvent stage, events larger than 16MB will be split into multiple events and contain the following information about which fragment the current event is.
Optional
txnThe transaction number. Only present if the operation is part of a multi-document transaction.
NOTE: txnNumber can be a Long if promoteLongs is set to false
See
https://www.mongodb.com/docs/manual/reference/change-events/#dropdatabase-event