[jira] [Updated] (ZOOKEEPER-3037) Add JvmPauseMonitor to ZooKeeper

["Mate Szalay-Beko (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-3037?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mate Szalay-Beko updated ZOOKEEPER-3037:
----------------------------------------
    Affects Version/s: 3.5.0
                       3.4.0
                           (was: 3.5.3)
                           (was: 3.4.12)

> Add JvmPauseMonitor to ZooKeeper
> --------------------------------
>
>                 Key: ZOOKEEPER-3037
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3037
>             Project: ZooKeeper
>          Issue Type: Improvement
>          Components: contrib
>    Affects Versions: 3.4.0, 3.5.0
>            Reporter: Norbert Kalmár
>            Assignee: Norbert Kalmár
>            Priority: Minor
>              Labels: pull-request-available
>             Fix For: 3.6.0
>
>          Time Spent: 2.5h
>  Remaining Estimate: 0h
>
> After a ZK crash, or client timeout sometimes it's hard to determine from the logs what happened. Knowing if ZK was responsive at the time would help a lot. For example, ZK might spend a lot of time waiting on GC (there is still some misconception that ZK is a storage). 
> To help detect this, HADOOP already has a great tool called JVM Pause Monitor. (As the name suggest, it can be also used for monitoring, but it also helps post-mortem in a lot of cases). Basically it has a daemon that sleeps for one second, and if the sleep time exceeds the 1s by more than the threshold (1s: INFO, 10s: WARN by default - this can be configurable in our case, see below), it will alert/make a log entry. It can also monitor the time GC took.
> The class implementing this is in HADOOP-common, but ZK should not depend on this package. Since this is a straightforward implementation, and in the past five years the few commits it had is nothing really serious, I think we could just copy this class in ZooKeeper, and introduce it as a configurable feature, by default it can be off.
> The class:
> https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/JvmPauseMonitor.java
> Task:
> - Create a class in ZK (under zookeeper/server/util/) called JvmPauseMonitor. 
> - Make feature configurable, by default: OFF
> - Make sleep time and threshold time configurable
> - Update documentation
> - Add [current size of the heap OR % of heap used] in the log entry whenever sleep threshold had exceeded by a lot (10s)



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