[GitHub] [druid] jihoonson commented on issue #9768: Allow minor compaction for non-consecutive segments

[GitBox <gi...@apache.org>]

jihoonson commented on issue #9768:
URL: https://github.com/apache/druid/issues/9768#issuecomment-904200393


   Assuming that we will keep the current segment ID allocation protocol that monotonically increases the partition ID on task failures, the problem we want to solve is, given a missing partitionId, how we would know whether the segment of that ID really doesn't exist or it is being created by some other task. One way to do is modifying the compaction task to as below.
   
   1) When some missing partitionIds are found, the compaction task tries to lock them using the regular locking mechanism.
   2) If the locking succeeds, the compaction task can safely assume that those partitionIds will never be used since there is no ingestion task creating segments of those partitionIds. In this case, the compaction task can simply ignore those missing partitionIds and compact the given segments all together.
   3) If the locking fails, there should be some ingestion task creating the segments of those partitionIds. In this case, the compaction task can split the input segments into multiple groups where each group has only consecutive partitionIds, and compact each group separately. Those segments that are being created by other task can be compacted later using another compaction task.


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