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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HDFS-14535) The default 8KB buffer in requestFileDescriptors#BufferedOutputStream is causing lots of heap allocation in HBase when using short-circut read
Date Tue, 04 Jun 2019 15:49:00 GMT

     [ https://issues.apache.org/jira/browse/HDFS-14535?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon resolved HDFS-14535.
--------------------------------
       Resolution: Fixed
     Hadoop Flags: Reviewed
    Fix Version/s: 3.3.0

> The default 8KB buffer in requestFileDescriptors#BufferedOutputStream is causing lots
of heap allocation in HBase when using short-circut read
> ----------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-14535
>                 URL: https://issues.apache.org/jira/browse/HDFS-14535
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Zheng Hu
>            Assignee: Zheng Hu
>            Priority: Major
>             Fix For: 3.3.0
>
>         Attachments: HDFS-14535.patch
>
>
> Our HBase team are trying to read the blocks from HDFS into pooled offheap ByteBuffers
directly (HBASE-21879),  and recently we had some benchmark, found that almost 45% heap allocation
from the DFS client.   The heap allocation flame graph can be see here: https://issues.apache.org/jira/secure/attachment/12970295/async-prof-pid-25042-alloc-2.svg
> After checking the code path,  we found that when requesting file descriptors from a
DomainPeer,  we allocated huge 8KB buffer for BufferedOutputStream, though the protocal content
was quite small and just few bytes.
> It made a heavy GC pressure for HBase when cacheHitRatio < 60%,  which increased the
HBase P999 latency.  Actually,  we can pre-allocate a small buffer for the BufferedOutputStream,
such as 512 bytes, it's enough to read the short-circuit fd protocal content.  we've created
a patch like that, and the allocation flame graph show that  after the patch, the heap allocation
from DFS client dropped from 45% to 27%, that's a very good thing  I think.  see: https://issues.apache.org/jira/secure/attachment/12970475/async-prof-pid-24534-alloc-2.svg
> Hope this attached patch can be merged into HDFS trunk, also Hadoop-2.8.x,  HBase will
benifit a lot from this. 
> Thanks. 
> For more details, can see here: https://issues.apache.org/jira/browse/HBASE-22387?focusedCommentId=16851639&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16851639



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