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From "Arun Suresh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-2962) ZKRMStateStore: Limit the number of znodes under a znode
Date Mon, 04 May 2015 05:56:07 GMT

    [ https://issues.apache.org/jira/browse/YARN-2962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14526289#comment-14526289

Arun Suresh commented on YARN-2962:

bq. we can simplify it without special hierarchies by having RM recursively read nodes all
the time. As we already specifically look for "application_" prefix to read app-date, having
application_1234_0456 right next to a 00/ directory is simply going to work without much complexity
Hmmm.. Currently, while reading, the code expects only leaf nodes to have data. We could modify
it to continue to child nodes while loading RMState. But updates to an app state would require
some thought. Consider updating state of app Id _1000000. The update code would have to first
check both the /.._1000000 and /.._10000/00 znodes. Also, retrieving state during load_all
and update_single might be hairy.. there can be ambiguous paths since a node path might not
be unique across the 2 schemes. For eg. /.._10000 will exist both in the new and old scheme.
In the old scheme it can contain data, but in the new scheme it shouldnt (it is an intermediate
node for /.._10000/\[00-99\])..

Although option 2 can be done, I'd prefer the your first suggestion (storing under RM_APP_ROOT/hierarchies).
We can have the RM read the old style but new apps and updates to old apps will go under the
new root. We can even delete the old scheme root if no children exist.

> ZKRMStateStore: Limit the number of znodes under a znode
> --------------------------------------------------------
>                 Key: YARN-2962
>                 URL: https://issues.apache.org/jira/browse/YARN-2962
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: resourcemanager
>    Affects Versions: 2.6.0
>            Reporter: Karthik Kambatla
>            Assignee: Varun Saxena
>            Priority: Critical
>         Attachments: YARN-2962.01.patch, YARN-2962.2.patch, YARN-2962.3.patch
> We ran into this issue where we were hitting the default ZK server message size configs,
primarily because the message had too many znodes even though they individually they were
all small.

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