Every mutation (Add/Update/Delete) has a transaction-id (incremental long)
assigned by our Messaging Queue (Kafka)
To index these mutations, an indexer thread pulls data from the queue, adds
& commits to IndexWriter, then updates the latest transaction-id in an
external system (ZooKeeper). During rollback/server-restarts, the threads
read the previous value from ZK & resume...
Have now moved to NRT implementation, where commit thread runs in the
background & am unable to find the latest transaction-id that got committed
Initially thought of adding transaction-id as a first-class field of the
index itself & then writing a custom-codec to harvest it, but this fails
when a mutation-set consists only of deletes [as there is no way to pass
these ids via IW delete APIs]
Is there a way to store this as part of segment-info?. Can setCommitData()
of IW help me here in any way?