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https://issues.apache.org/jira/browse/HDFS-7129?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14152215#comment-14152215
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Chris Nauroth commented on HDFS-7129:
-------------------------------------
Nice work, Xiaoyu. Just a couple more comments in addition to the great
feedback Arpit already gave:
# {{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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