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https://issues.apache.org/jira/browse/HDFS-14308?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joe McDonnell updated HDFS-14308:
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Attachment: ec_heap_dump.png
> DFSStripedInputStream should implement unbuffer()
> -------------------------------------------------
>
> Key: HDFS-14308
> URL: https://issues.apache.org/jira/browse/HDFS-14308
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 3.0.0
> Reporter: Joe McDonnell
> Priority: Major
> Attachments: ec_heap_dump.png
>
>
> Some users of HDFS cache opened HDFS file handles to avoid repeated
> roundtrips to the NameNode. For example, Impala caches up to 20,000 HDFS file
> handles by default. Recent tests on erasure coded files show that the open
> file handles can consume a large amount of memory when not in use.
> For example, here is output from Impala's JMX endpoint when 608 file handles
> are cached
> {noformat}
> {
> "name": "java.nio:type=BufferPool,name=direct",
> "modelerType": "sun.management.ManagementFactoryHelper$1",
> "Name": "direct",
> "TotalCapacity": 1921048960,
> "MemoryUsed": 1921048961,
> "Count": 633,
> "ObjectName": "java.nio:type=BufferPool,name=direct"
> },{noformat}
> This shows direct buffer memory usage of 3MB per DFSStripedInputStream.
> Attached is output from Eclipse MAT showing that the direct buffers come from
> DFSStripedInputStream objects.
> To support caching file handles on erasure coded files, DFSStripedInputStream
> should implement the unbuffer() call. See HDFS-7694. "unbuffer()" is intended
> to move an input stream to a lower memory state to support these caching use
> cases. Both Impala and HBase call unbuffer() when a file handle is being
> cached and potentially unused for significant chunks of time.
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