[OAK-3904] Compaction Map predicate should use cached state for evaluation

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.2.17, 1.3.15, 1.4
• Component/s: segmentmk
• Labels: compaction gc
• Epic Link: SegmentMK revision GC
• Assignee: Alex Deparvu
• Reporter: Alex Deparvu
• Created: 21/Jan/16 09:25
• Updated: 23/Jun/16 14:56
• Resolved: 21/Jan/16 09:35

Description

In the case of offline compaction, the Compactor predicate would try to evaluate if a specific node is candidate for the map of not based on a set of conditions.
To evaluate said conditions, the predicate currently uses the compacted state, the one that was just written by the SegmentWriter [0], but this offers very poor performance as this NodeState will be accessed from the TarWriter directly, a very IO intensive call (no memory mapping, no caching of the segment) [1].
A much better thing is to use the cached nodestate, in my local test (on a SSD) this accounts for 10% of perf loss, I would imagine the gains are more significant on a non-SSD disk.

[0] https://github.com/apache/jackrabbit-oak/blob/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/Compactor.java#L252
[1] https://github.com/apache/jackrabbit-oak/blob/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/file/TarWriter.java#L190