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From "Francesco Mari (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-4812) Reduce calls to SegmentStore#newSegmentId from the Segment class
Date Thu, 15 Sep 2016 09:11:21 GMT

    [ https://issues.apache.org/jira/browse/OAK-4812?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15492820#comment-15492820
] 

Francesco Mari commented on OAK-4812:
-------------------------------------

I guess the record ID cache per segment is kind of useless. It should better be a segment
ID cache, since this seems to be the bulk of the problem. Creating record IDs is cheap, but
it's not the same for segment IDs.

> Reduce calls to SegmentStore#newSegmentId from the Segment class
> ----------------------------------------------------------------
>
>                 Key: OAK-4812
>                 URL: https://issues.apache.org/jira/browse/OAK-4812
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segment-tar
>            Reporter: Alex Parvulescu
>            Priority: Minor
>
> 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



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