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https://issues.apache.org/jira/browse/HDFS-3246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16781270#comment-16781270
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Zheng Hu commented on HDFS-3246:
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bq. what benchmarks or tools would you run to ensure it reduces GC overhead?
As the HBASE-21879 said, we are observing GC pressure at HBase side when
running YCSB benchmark. Amost all of the HBase read/write path are offheap now,
except here: pread a HBase data block from HDFS, because of the lack of the
ByteBuffer pread interface, so HBase can only read a data block into heap (see
[1]). In 100% Get case, graph [2] and [3] indicated that the p999 latency was
almost the same as the G1 Young GC STW ( ~ 100ms). so we have the reason to
believe that the onheap pread increase GC overhead. while if verify the
reducing GC overhead by using HBase, seems not a good way , its stack is too
deep and so many variables, any simple HDFS tools ?
(Of course, I'll give a final benchmark after HBASE-21879 fixed, but it will
take some time, and this issue need to be fixed firstly)
1. http://openinx.github.io/images/hbase-offheap-onheap.png
2.
https://issues.apache.org/jira/secure/attachment/12958391/gc-data-before-HBASE-21879.png
3.
https://issues.apache.org/jira/secure/attachment/12958487/QPS-latencies-before-HBASE-21879.png
> pRead equivalent for direct read path
> -------------------------------------
>
> Key: HDFS-3246
> URL: https://issues.apache.org/jira/browse/HDFS-3246
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client, performance
> Affects Versions: 3.0.0-alpha1
> Reporter: Henry Robinson
> Assignee: Sahil Takiar
> Priority: Major
> Attachments: HDFS-3246.001.patch, HDFS-3246.002.patch,
> HDFS-3246.003.patch, HDFS-3246.004.patch
>
>
> There is no pread equivalent in ByteBufferReadable. We should consider adding
> one. It would be relatively easy to implement for the distributed case
> (certainly compared to HDFS-2834), since DFSInputStream does most of the
> heavy lifting.
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