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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7129) Metrics to track usage of memory for writes
Date Mon, 29 Sep 2014 20:26:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7129?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14152215#comment-14152215

Chris Nauroth commented on HDFS-7129:

Nice work, Xiaoyu.  Just a couple more comments in addition to the great feedback Arpit already
# {{RamDiskReplicaLruTracker}}: I see the patch adds an import of {{Time}}, but it's not used.
 Was the intention to use {{Time#monotonicNow}} throughout this class?  The class currently
uses {{System#currentTimeMillis}}, which would put the eviction logic at more risk of an imprecise
timer or resetting the system clock.
# {{TestLazyPersistFiles#startUpCluster}}: I recommend calling {{fail}} if {{initJMX}} throws
an exception instead of logging and continuing.  If JMX initialization fails, then it's highly
likely that the tests will fail later on the metrics assertions.  Failing earlier would help
a dev find the root cause faster.

> Metrics to track usage of memory for writes
> -------------------------------------------
>                 Key: HDFS-7129
>                 URL: https://issues.apache.org/jira/browse/HDFS-7129
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode
>    Affects Versions: HDFS-6581
>            Reporter: Arpit Agarwal
>            Assignee: Xiaoyu Yao
>         Attachments: HDFS-7129.0.patch, HDFS-7129.1.patch
> A few metrics to evaluate feature usage and suggest improvements. Thanks to [~sureshms]
for some of these suggestions.
> # Number of times a block in memory was read (before being ejected)
> # Average block size for data written to memory tier
> # Time the block was in memory before being ejected
> # 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).
> # Replicas written to disk by lazy writer
> # Bytes written to disk by lazy writer
> # Replicas deleted by application before being persisted to disk

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