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https://issues.apache.org/jira/browse/OAK-7259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16378532#comment-16378532
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Michael Dürig commented on OAK-7259:
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I share [~frm] concerns re. {{updateCommitsCountMap()}} not being thread safe
and I think this is not comparable with {{ConcurrentHashMap}}. Concurrent calls
to {{updateCommitsCountMap()}} might lead to an incoherent state that is non
transient. However, I also share [~dulceanu] concerns re. adding additional
potential contention points on the "commit path". As an alternative, couldn't
we move the chore of updating {{commitsCountMap}} to the consumer thread
calling {{SegmentNodeStoreStats.getCommitsCountPerWriter()}}? My idea would be
to queue pending {{writernNames}} s that would otherwise be directly passed to
{{updateCommitsCountMap()}} and batch process them in calls to
{{getCommitsCountPerWriter()}}. IMO a good starting point would be to move all
related logic to its own class as [~frm] suggested as well.
>From the peanut gallery:
* {{Thread.getStackTrace()}} is expensive. We need to understand whether this
is problematic in this context or not. Starting with Java 9 there is
{{StackWalker}}, which is supposed to be cheaper. Until then, we should
probably have a way to switch collecting stack traces off.
* Can we unify {{SegmentNodeStoreStats.dequeuedAfter()}} and
{{SegmentNodeStoreStats.onCommitDequeued()}}?
* I would prefer to return an empty table from
{{SegmentNodeStoreStatsMBean.getCommitsCountPerWriter()}} and
{{SegmentNodeStoreStatsMBean.getQueuedWriters()}} instead of throwing an
{{OpenDataException}}.
* Just an idea for now, can (should?) we make
{{SegmentNodeStoreStats.commitsCountMapMaxSize}} configurable through a setter
in {{SegmentNodeStoreStatsMBean}}?
> 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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