[jira] [Created] (OAK-4483) Remove synchronized access requirement from MetricStatisticsProvider#getStats

["Chetan Mehrotra (JIRA)" <ji...@apache.org>]

Chetan Mehrotra created OAK-4483:
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             Summary: Remove synchronized access requirement from MetricStatisticsProvider#getStats
                 Key: OAK-4483
                 URL: https://issues.apache.org/jira/browse/OAK-4483
             Project: Jackrabbit Oak
          Issue Type: Improvement
          Components: core
    Affects Versions: 1.4
            Reporter: Chetan Mehrotra
            Assignee: Chetan Mehrotra
             Fix For: 1.6, 1.4.4


{{MetricStatisticsProvider}} makes {{getStats}} as synchronized. This can cause contention in concurrent scenarios specially when lots of Sessions are created as the stats instance are looked at time of session creation

{noformat}
"qtp618865225-3444" #3444 prio=5 os_prio=0 tid=0x00007f7fe5083800 nid=0x7629 waiting for monitor entry [0x00007f7fdb9f7000]
   java.lang.Thread.State: BLOCKED (on object monitor)
	at org.apache.jackrabbit.oak.plugins.metric.MetricStatisticsProvider.getStats(MetricStatisticsProvider.java:129)
	- waiting to lock <0x00000003c1bfb1d0> (a org.apache.jackrabbit.oak.plugins.metric.MetricStatisticsProvider)
	at org.apache.jackrabbit.oak.plugins.metric.MetricStatisticsProvider.getCounterStats(MetricStatisticsProvider.java:107)
	at org.apache.jackrabbit.oak.stats.StatisticManager.getStatsCounter(StatisticManager.java:99)
	at org.apache.jackrabbit.oak.jcr.session.SessionStats.<init>(SessionStats.java:83)
	at org.apache.jackrabbit.oak.jcr.delegate.SessionDelegate.<init>(SessionDelegate.java:150)
	at org.apache.jackrabbit.oak.jcr.repository.RepositoryImpl$1.<init>(RepositoryImpl.java:301)
	at org.apache.jackrabbit.oak.jcr.repository.RepositoryImpl.createSessionDelegate(RepositoryImpl.java:299)
	at org.apache.jackrabbit.oak.jcr.repository.RepositoryImpl.login(RepositoryImpl.java:281)
	at com.adobe.granite.repository.impl.CRX3RepositoryImpl.login(CRX3RepositoryImpl.java:94)
{noformat}

Instead of current approach it should use ConcurrentHashMap and still ensure that duplicate metric instance did not get created





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