[jira] [Created] (HDFS-14370) Edit log tailing fast-path should allow for backoff

["Erik Krogen (JIRA)" <ji...@apache.org>]

Erik Krogen created HDFS-14370:
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             Summary: 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


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 reported 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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