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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2770) ZooKeeper slow operation log
Date Fri, 09 Mar 2018 07:33:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2770?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16392529#comment-16392529
] 

ASF GitHub Bot commented on ZOOKEEPER-2770:
-------------------------------------------

Github user zodvik commented on the issue:

    https://github.com/apache/zookeeper/pull/307
  
    > reasons why any given read or write operation may become slow: a software bug, a
protocol problem, a hardware issue with the commit log(s), a network issue. If the problem
is constant it is trivial to come to an understanding of the cause. However in order to diagnose
intermittent problems we often don't know where, or when, to begin looking. We need some sort
of timestamped indication of the problem
    
    IMO, slow query log is useful for those systems were the response times can vary due to
type of query (long scans, improper index, poor query plan, etc.). For the type of issues
mentioned, we can expect all operations to be impacted and fill up the log. 
    
    If the intent is to get an time stamp indication of the problem, a metric reporting mechanism
will be more useful. If we have rolling interval percentiles (per command?) published either
to `stat` or `jmx`, that would give a good visibility.



> ZooKeeper slow operation log
> ----------------------------
>
>                 Key: ZOOKEEPER-2770
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2770
>             Project: ZooKeeper
>          Issue Type: Improvement
>            Reporter: Karan Mehta
>            Assignee: Karan Mehta
>            Priority: Major
>         Attachments: ZOOKEEPER-2770.001.patch, ZOOKEEPER-2770.002.patch, ZOOKEEPER-2770.003.patch
>
>
> ZooKeeper is a complex distributed application. There are many reasons why any given
read or write operation may become slow: a software bug, a protocol problem, a hardware issue
with the commit log(s), a network issue. If the problem is constant it is trivial to come
to an understanding of the cause. However in order to diagnose intermittent problems we often
don't know where, or when, to begin looking. We need some sort of timestamped indication of
the problem. Although ZooKeeper is not a datastore, it does persist data, and can suffer intermittent
performance degradation, and should consider implementing a 'slow query' log, a feature very
common to services which persist information on behalf of clients which may be sensitive to
latency while waiting for confirmation of successful persistence.
> Log the client and request details if the server discovers, when finally processing the
request, that the current time minus arrival time of the request is beyond a configured threshold.

> Look at the HBase {{responseTooSlow}} feature for inspiration. 



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