[jira] [Created] (OAK-3362) Estimate compaction based on diff to previous compacted head state

["Alex Parvulescu (JIRA)" <ji...@apache.org>]

Alex Parvulescu created OAK-3362:
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             Summary: Estimate compaction based on diff to previous compacted head state
                 Key: OAK-3362
                 URL: https://issues.apache.org/jira/browse/OAK-3362
             Project: Jackrabbit Oak
          Issue Type: Sub-task
          Components: segmentmk
            Reporter: Alex Parvulescu
            Priority: Minor


Food for thought: try to base the compaction estimation on a diff between the latest compacted state and the current state.

Pros
* estimation duration would be proportional to number of changes on the current head state
* using the size on disk as a reference, we could actually stop the estimation early when we go over the gc threshold.
* data collected during this diff could in theory be passed as input to the compactor so it could focus on compacting a specific subtree

Cons
* need to keep a reference to a previous compacted state. post-startup and pre-compaction this might prove difficult (except maybe if we only persist the revision similar to what the async indexer is doing currently)
* coming up with a threshold for running compaction might prove difficult
* diff might be costly, but still cheaper than the current full diff





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