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From "Erik Krogen (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-14370) Edit log tailing fast-path should allow for backoff
Date Fri, 02 Aug 2019 17:59:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-14370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16899090#comment-16899090
] 

Erik Krogen edited comment on HDFS-14370 at 8/2/19 5:58 PM:
------------------------------------------------------------

Thanks [~vagarychen]! The description did mention that negative values disable the backoff
behavior, but I made it more clear that this is the default in the v003 patch.

[~ayushtkn], I will commit this early next week unless I hear back from you, please let me
know if you have any concerns with the v003 patch.


was (Author: xkrogen):
Thanks [~vagarychen]! The description did mention that negative values disable the backoff
behavior, but I made it more clear that this is the default.

[~ayushtkn], I will commit this early next week unless I hear back from you, please let me
know if you have any concerns with the v003 patch.

> Edit log tailing fast-path should allow for backoff
> ---------------------------------------------------
>
>                 Key: HDFS-14370
>                 URL: https://issues.apache.org/jira/browse/HDFS-14370
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode, qjm
>    Affects Versions: 3.3.0
>            Reporter: Erik Krogen
>            Assignee: Erik Krogen
>            Priority: Major
>         Attachments: HDFS-14370.000.patch, HDFS-14370.001.patch, HDFS-14370.002.patch,
HDFS-14370.003.patch
>
>
> As part of HDFS-13150, in-progress edit log tailing was changed to use an RPC-based mechanism,
thus allowing the edit log tailing frequency to be turned way down, and allowing standby/observer
NameNodes to be only a few milliseconds stale as compared to the Active NameNode.
> When there is a high volume of transactions on the system, each RPC fetches transactions
and takes some time to process them, self-rate-limiting how frequently an RPC is submitted.
In a lightly loaded cluster, however, most of these RPCs return an empty set of transactions,
consuming a high (de)serialization overhead for very little benefit. This was reported by
[~jojochuang] in HDFS-14276 and I have also seen it on a test cluster where the SbNN was submitting
8000 RPCs per second that returned empty.
> I propose we add some sort of backoff to the tailing, so that if an empty response is
received, it will wait a longer period of time before submitting a new RPC.



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