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From Michael Dürig (JIRA) <j...@apache.org>
Subject [jira] [Commented] (OAK-7668) Optimization: SegmentNodeState#fastEquals should compare getStableIdBytes instead of getStableId
Date Fri, 03 Aug 2018 07:52:00 GMT

    [ https://issues.apache.org/jira/browse/OAK-7668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16567910#comment-16567910
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Michael Dürig commented on OAK-7668:
------------------------------------

[~jsedding], I have seen this method coming up in stack traces before. So far only in quite
artificial tests, never in a production like scenario. Likely because in most production cases
the code path that requires comparing stable ids is cut short by the code [preceding it|https://github.com/apache/jackrabbit-oak/blob/trunk/oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/SegmentNodeState.java#L650].


Would be good to have a benchmark that (roughly) simulates package installation. This would
allow to understand the effect of the proposed optimisation. Do you think you could come up
with something?

> Optimization: SegmentNodeState#fastEquals should compare getStableIdBytes instead of
getStableId
> ------------------------------------------------------------------------------------------------
>
>                 Key: OAK-7668
>                 URL: https://issues.apache.org/jira/browse/OAK-7668
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segment-tar
>    Affects Versions: 1.9.6
>            Reporter: Julian Sedding
>            Priority: Minor
>
> I have observed via stack trace sampling that during the installation of a Vault package
with many small nodes on an otherwise quiet system, about 1/4 of stack traces had the following
lines on the top (this was on Oak 1.6.11, but reading the code it applies equally on trunk):
> {code}
> at java.lang.String.valueOf(String.java:2994)
> at java.lang.StringBuilder.append(StringBuilder.java:131)
> at org.apache.jackrabbit.oak.segment.SegmentNodeState.getStableId(SegmentNodeState.java:124)+
> at org.apache.jackrabbit.oak.segment.SegmentNodeState.fastEquals(SegmentNodeState.java:632)
> ...
> {code}
> I suggest comparing the result of {{SegmentNodeState#getStableIdBytes}} instead of {{SegmentNodeState#getStableId}},
which bypasses building the String representation.
> So far I have no proof in the form of a benchmark, but it seems quite clear that this
change will result in less work being performed.



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