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https://issues.apache.org/jira/browse/HDFS-14370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16899288#comment-16899288
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Ayush Saxena commented on HDFS-14370:
-------------------------------------
Thanx [~xkrogen] for the patch. Really sorry for the delay, Almost LGTM.
As per the code the back-off gets disabled with value 0 too.
{code:java}
+ * performed but no edits are available to be read. If this is less than or
+ * equal to 0, backoff is disabled.
{code}
Shouldn't we set the default as 0 itself rather than using negative value,
Makes more sense Mathematically, a Zero max compared to a negative max.
Secondly, we should mention this config in
{{ObserverNameNode.html#Configurations}}
> 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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