Alex Parvulescu created OAK-2654:
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Summary: SegmentIdTable too eager to refresh
Key: OAK-2654
URL: https://issues.apache.org/jira/browse/OAK-2654
Project: Jackrabbit Oak
Issue Type: Improvement
Components: segmentmk
Reporter: Alex Parvulescu
Assignee: Alex Parvulescu
Calling SegmentIdTable#getSegmentId might trigger a reference table refresh if
a certain condition is met, I think that this condition is too eager to trigger
the refresh and in high write scenarios, this results in large pauses as the
method is synchronized.
The current condition resembles a cache miss (_index != first_) which means
that when looking up a segment id by the _lsb_ it might happen that it either
- is not there, so it needs to be added (no refresh on this branch)
- or there is an overlap on lsb values (actually on the value returned by
_getIndex(lsb)_), in which case a refresh will be triggered.
In high write scenarios the refresh case happens a lot more frequently so a
refresh is triggered, even if it might not be needed. a refresh makes sense
when there are null references and it might make sense for them to be collected
otherwise we're just creating clones of the same map over and over again.
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