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https://issues.apache.org/jira/browse/HADOOP-11708?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14358999#comment-14358999
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Sean Busbey commented on HADOOP-11708:
--------------------------------------
(We could also just remove the synchronization from DFSOutputStream, release
note the change, and require HBase to correct its behavior)
> CryptoOutputStream synchronization differences from DFSOutputStream break
> HBase
> -------------------------------------------------------------------------------
>
> Key: HADOOP-11708
> URL: https://issues.apache.org/jira/browse/HADOOP-11708
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs
> Affects Versions: 2.6.0
> Reporter: Sean Busbey
> Assignee: Sean Busbey
> Priority: Critical
>
> For the write-ahead-log, HBase writes to DFS from a single thread and sends
> sync/flush/hflush from a configurable number of other threads (default 5).
> FSDataOutputStream does not document anything about being thread safe, and it
> is not thread safe for concurrent writes.
> However, DFSOutputStream is thread safe for concurrent writes + syncs. When
> it is the stream FSDataOutputStream wraps, the combination is threadsafe for
> 1 writer and multiple syncs (the exact behavior HBase relies on).
> When HDFS Transparent Encryption is turned on, CryptoOutputStream is inserted
> between FSDataOutputStream and DFSOutputStream. It is proactively labeled as
> not thread safe, and this composition is not thread safe for any operations.
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