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https://issues.apache.org/jira/browse/HDFS-5498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13825886#comment-13825886
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Kihwal Lee commented on HDFS-5498:
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For quick restart (e.g. rolling upgrade), the initialization of
{{BlockPoolSlice}} can be made fater by cashing {{dfsUsed}}. Currently DU
unconditionally runs the du command in its constructor. Filed HADOOP-10111 to
add an option to specify an initial "used" value and delay the initial scan.
When I incorporated this change in {{BlockPoolSlice}}, the initialization time
for each volume became several milliseconds on restart. It looks for the cache
file and use the value if it is less than 5 minutes old (the default DU
interval).
Another part of start-up time improvement will come from parallelizing the
scanning & popuating {{ReplicaMap}}.
> Improve datanode startup time
> -----------------------------
>
> Key: HDFS-5498
> URL: https://issues.apache.org/jira/browse/HDFS-5498
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Kihwal Lee
>
> Similarly to HDFS-5027, an improvement can be made for getVomeMap(). This is
> the phase in which ReplicaMap.is populated. But it will be even better if
> datanode scans only once and do both.
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