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Tsuyoshi OZAWA commented on HDFS-4953: -------------------------------------- bq. Setting dfs.client.mmap.cache.size to 0 will prevent mmap from happening. bq. If mmap does not provide a performance improvement on that platform, users of that platform can disable it. OK. Then we should document them explicitly. Should we create new JIRA to do that? > enable HDFS local reads via mmap > -------------------------------- > > Key: HDFS-4953 > URL: https://issues.apache.org/jira/browse/HDFS-4953 > Project: Hadoop HDFS > Issue Type: New Feature > Affects Versions: 2.3.0 > Reporter: Colin Patrick McCabe > Assignee: Colin Patrick McCabe > Attachments: benchmark.png, HDFS-4953.001.patch, HDFS-4953.002.patch, > HDFS-4953.003.patch, HDFS-4953.004.patch, HDFS-4953.005.patch > > > Currently, the short-circuit local read pathway allows HDFS clients to access > files directly without going through the DataNode. However, all of these > reads involve a copy at the operating system level, since they rely on the > read() / pread() / etc family of kernel interfaces. > We would like to enable HDFS to read local files via mmap. This would enable > truly zero-copy reads. > In the initial implementation, zero-copy reads will only be performed when > checksums were disabled. Later, we can use the DataNode's cache awareness to > only perform zero-copy reads when we know that checksum has already been > verified. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira