fix: use start_after instead of resume_after for change stream tokens if MongoDB version >= 4.2 #23
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This tap has had some issues in log-based replication mode and I've been trying to chase those down and make this resilient in the face of all scenarios. This PR updates the "resume change stream" handling that is used when the tap is running in log-based mode using a saved bookmark (that is, when not in "full refresh" mode).
Previously the tap was passing the saved resume token from the meltano state to the "open change stream" command in the
resume_afterfield. This field is supported by all versions of MongoDB change streams (MongoDB 3.6 and above).In MongoDB 4.2, a new
start_afterfield was added to the "open change stream" command. This is preferable toresume_afterfor this tap's use cases, so this PR uses thestart_afterfield if the MongoDB version is 4.2 or greater.Why is
start_afterpreferable? See the docs: https://www.mongodb.com/docs/manual/changeStreams/#startafter-for-change-streams But tl;dr: If a given resume token is not present in the oplog (which can happen if this tap has not been run in X hours, where X > oplog headroom in hours),start_afterwill gracefully open a new change stream, whileresume_afterwill error.