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https://issues.apache.org/jira/browse/HADOOP-10694?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14621740#comment-14621740
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Gopal V commented on HADOOP-10694:
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[~ozawa]: I think the synchronization is unintentional, since two threads using
DataInputBuffer readers without synchronization would cause corruption
(something like readInt() would result in interleaved corruption, because each
byte read() is independently synchronized).
> Remove synchronized input streams from Writable deserialization
> ---------------------------------------------------------------
>
> Key: HADOOP-10694
> URL: https://issues.apache.org/jira/browse/HADOOP-10694
> Project: Hadoop Common
> Issue Type: Bug
> Components: io
> Reporter: Gopal V
> Assignee: Gopal V
> Labels: BB2015-05-TBR
> Attachments: HADOOP-10694.1.patch, writable-read-sync.png
>
>
> Writable deserialization is slowing down due to a synchronized block within
> DataInputBuffer$Buffer.
> ByteArrayInputStream::read() is synchronized and this shows up as a slow
> uncontested lock.
> Hive ships with its own faster thread-unsafe version with
> hive.common.io.NonSyncByteArrayInputStream.
> !writable-read-sync.png!
> The DataInputBuffer and Writable deserialization should not require a lock
> per readInt()/read().
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