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https://issues.apache.org/jira/browse/HDFS-17593?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Csaba Ringhofer updated HDFS-17593:
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Description:
The HDFS client seems to always get block locations from the namenode when
opening a file:
https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java#L1099
This leads to unnecessary RPCs in Apache Impala when doing reads, as the block
locations are cached globally and the executors already have a good guess about
the block locations when opening a stream. Unless the cached block locations
are stale ideally no RPC should be made to the namenode.
was:
The HDFS client seems to always get block locations from the namenode when
opening a file:
https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java#L1099
This leads to unnecessary RPCs in Apache Impala when doing remote reads, as the
block locations are cached globally and the executors already have a good guess
about the block locations when opening a stream. Unless the cached block
locations are stale ideally no RPC should be made to the namenode.
> Allow setting block locations when opening streams
> --------------------------------------------------
>
> Key: HDFS-17593
> URL: https://issues.apache.org/jira/browse/HDFS-17593
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Csaba Ringhofer
> Priority: Major
>
> The HDFS client seems to always get block locations from the namenode when
> opening a file:
> https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java#L1099
> This leads to unnecessary RPCs in Apache Impala when doing reads, as the
> block locations are cached globally and the executors already have a good
> guess about the block locations when opening a stream. Unless the cached
> block locations are stale ideally no RPC should be made to the namenode.
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