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From "Arpit Agarwal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6581) Write to single replica in memory
Date Mon, 22 Sep 2014 21:38:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14143872#comment-14143872
] 

Arpit Agarwal commented on HDFS-6581:
-------------------------------------

Suresh, good suggestions. Let me file a task for metrics. A few other metrics I have been
thinking of:
# Number of blocks written to memory
# Number of memory writes requested but not satisfied (failed-over to disk)
# Number of blocks evicted without ever being read from memory
# Average delay between memory write and disk write (window where a node restart could cause
data loss).

It might be also useful to track how often a block was requested to be read shortly after
eviction, however that requires more overhead to track.

We can do this work in trunk.

> Write to single replica in memory
> ---------------------------------
>
>                 Key: HDFS-6581
>                 URL: https://issues.apache.org/jira/browse/HDFS-6581
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>            Reporter: Arpit Agarwal
>            Assignee: Arpit Agarwal
>         Attachments: HDFS-6581.merge.01.patch, HDFS-6581.merge.02.patch, HDFS-6581.merge.03.patch,
HDFS-6581.merge.04.patch, HDFS-6581.merge.05.patch, HDFS-6581.merge.06.patch, HDFS-6581.merge.07.patch,
HDFS-6581.merge.08.patch, HDFS-6581.merge.09.patch, HDFSWriteableReplicasInMemory.pdf, Test-Plan-for-HDFS-6581-Memory-Storage.pdf
>
>
> Per discussion with the community on HDFS-5851, we will implement writing to a single
replica in DN memory via DataTransferProtocol.
> This avoids some of the issues with short-circuit writes, which we can revisit at a later
time.



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