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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6982) nntop: top­-like tool for name node users
Date Thu, 13 Nov 2014 00:18:36 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14208968#comment-14208968
] 

Andrew Wang commented on HDFS-6982:
-----------------------------------

Haohui, IIUC your suggestion here is to use an exponential moving average. However, my understanding
is that there's no direct link between the alpha parameter and a time-based window, e.g. 1mi,
5 min, 30min. I think the time-based windows are more operator-friendly.

Also, considering that the purpose of this feature is to determine a ranked list of users
and what operations they're doing, the exact values aren't actually that important. IIUC the
situation you describe will lead to small errors, not big ones. If there are bigger correctness
issues, I think we can fix them by adding more synchronization. Thanks.

> nntop: top­-like tool for name node users
> -----------------------------------------
>
>                 Key: HDFS-6982
>                 URL: https://issues.apache.org/jira/browse/HDFS-6982
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>            Reporter: Maysam Yabandeh
>            Assignee: Maysam Yabandeh
>         Attachments: HDFS-6982.patch, HDFS-6982.v2.patch, HDFS-6982.v3.patch, HDFS-6982.v4.patch,
HDFS-6982.v5.patch, HDFS-6982.v6.patch, nntop-design-v1.pdf
>
>
> In this jira we motivate the need for nntop, a tool that, similarly to what top does
in Linux, gives the list of top users of the HDFS name node and gives insight about which
users are sending majority of each traffic type to the name node. This information turns out
to be the most critical when the name node is under pressure and the HDFS admin needs to know
which user is hammering the name node and with what kind of requests. Here we present the
design of nntop which has been in production at Twitter in the past 10 months. nntop proved
to have low cpu overhead (< 2% in a cluster of 4K nodes), low memory footprint (less than
a few MB), and quite efficient for the write path (only two hash lookup for updating a metric).



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