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https://issues.apache.org/jira/browse/OAK-7259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16380443#comment-16380443
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Andrei Dulceanu commented on OAK-7259:
--------------------------------------
In the branch previously shared [0], I made the following changes:
* extracted all the logic related to tracking writers in its own class,
{{CommitsTracker}}
* delegated logic for keeping last x writers to {{ConcurrentLinkedHashMap}}
(introduced dependency to {{com.googlecode.concurrentlinkedhashmap}} in
{{oak-parent}}; do we need to move this to {{oak-segment-tar}} only?)
* unified {{SegmentNodeStoreStats.dequeuedAfter()}} and
{{SegmentNodeStoreStats.onCommitDequeued()}} into a single method, as well as
{{SegmentNodeStoreStats.onCommit}} and SegmentNodeStoreStats.committedAfter()
{quote}
I would prefer to return an empty table from
SegmentNodeStoreStatsMBean.getCommitsCountPerWriter() and
SegmentNodeStoreStatsMBean.getQueuedWriters() instead of throwing an
OpenDataException.
{quote}
I couldn't find a reasonable solution for this, since having an empty {{data}}
map in either of the methods will result in an {{IllegalArgumentException}}
being raised. Any suggestions on how to avoid this?
{quote}
Just an idea for now, can (should?) we make
SegmentNodeStoreStats.commitsCountMapMaxSize configurable through a setter in
SegmentNodeStoreStatsMBean?
{quote}
The previous, custom logic for bookkeeping allowed changing the max size on the
fly, but switching to {{ConcurrentLinkedHashMap}} we lost this flexibility. If
this is truly needed, we could revisit the code (in a new issue?).
[~frm], [~mduerig] WDYT?
[0] https://github.com/dulceanu/jackrabbit-oak/tree/issues/OAK-7259
> Improve SegmentNodeStoreStats to include number of commits per thread and
> threads currently waiting on the semaphore
> --------------------------------------------------------------------------------------------------------------------
>
> Key: OAK-7259
> URL: https://issues.apache.org/jira/browse/OAK-7259
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: segment-tar
> Reporter: Andrei Dulceanu
> Assignee: Andrei Dulceanu
> Priority: Major
> Labels: tooling
> Fix For: 1.9.0, 1.10
>
>
> When investigating the performance of {{segment-tar}}, the source of the
> writes (commits) is a very useful indicator of the cause.
> To better understand which threads are currently writing in the repository
> and which are blocked on the semaphore, we need to improve
> {{SegmentNodeStoreStats}} to:
> * expose the number of commits executed per thread
> * expose threads currently waiting on the semaphore
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