[OAK-4812] Reduce calls to SegmentStore#newSegmentId from the Segment class

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: Segment Tar 0.0.14
• Component/s: segment-tar
• Assignee: Francesco Mari
• Reporter: Alex Deparvu
• Created: 15/Sep/16 08:56
• Updated: 10/Oct/16 11:32
• Resolved: 27/Sep/16 09:51

Description

OAK-4631 introduced a change in records handling in a segment that will amplify the number of calls to SegmentStore#newSegmentId by the number of external references [0]. It usually is the case that there are a lot of record references that point to the same segment id, and the existing recordIdCache would not help much in this case.
The scenario I'm seeing for offline compaction (might be a bit biased) is a full traversal of segments that increases pressure on the SegmentIdTable by calling newSegmentId with a lot of already existing segments.
I'm creating this issue as an 'Improvement' as I think it is interesting to look into reducing this pressure. This might be by squeezing more out of the SegmentIdTable bits (I'd like to followup on this with a benchmark) or revisiting the code paths from the Segment class.

[0] https://github.com/apache/jackrabbit-oak/blob/trunk/oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/Segment.java#L405

Issue Links

• is related to: OAK-4631 Simplify the format of segments and serialized records
• relates to: OAK-4844 Analyse effects of simplified record ids