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https://issues.apache.org/jira/browse/OAK-7262?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrei Dulceanu resolved OAK-7262.
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Resolution: Fixed
> LockBasedScheduler#getHeadNodeState poor performance due to lock contention
> in commitTimeHistogram implementation
> -----------------------------------------------------------------------------------------------------------------
>
> Key: OAK-7262
> URL: https://issues.apache.org/jira/browse/OAK-7262
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: segment-tar
> Reporter: Andrei Dulceanu
> Assignee: Andrei Dulceanu
> Priority: Major
> Fix For: 1.9.0, 1.10
>
>
> With OAK-4732, we slightly prioritised reads, allowing callers of
> {{LockBasedScheduler#getHeadNodeState}} to wait for a certain amount of time
> on the commit semaphore, in order to fetch the latest head. The amount of
> time to wait for was computed as the median of the latest 1000 commits, but
> the implementation was flexible enough to replace the 0.5 quantile with a
> different value.
> The initial implementation used {{SynchronizedDescriptiveStatistics}} from
> {{commons-math3}}. In OAK-6430, we replaced that with a {{Histogram}} backed
> by a {{SlindingWindowReservoir}} from the dropwizard metric library
> ({{io.dropwizard.metrics}}).
> One of the problems observed with the current implementation is that, under
> heavy loading, the performance of {{LockBasedScheduler#getHeadNodeState}}
> decreases due to lock contention in {{commitTimeHistogram}} implementation.
> Namely, {{SlidingWindowReservoir#getSnapshot}} seems to be a bottleneck. It
> copies an array of 1000 elements at each invocation of
> {{LockBasedScheduler#getHeadNodeState}}, acquiring and releasing a lock for
> each element in the array.
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