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https://issues.apache.org/jira/browse/HDFS-3979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13470823#comment-13470823
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Kan Zhang commented on HDFS-3979:
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bq. Why API4 is needed for HBase?
API3 or API4, it probably doesn't make a huge difference, IMHO. On the other
hand, assuming the performance penalty of going from API3 to API4 is
negligible, it's probably not worth complicating the code to support API3
(instead of API4).
bq. Lastly, we can play with this. For example only one of the replicas could
sync to disk and the other's just guarantee the data in the OS buffers (API4.5
).
Yes, it would be very interesting to see if it saves to sync only the local
replica or acknowledge to the client upon the first successful sync of any
replica.
> Fix hsync and hflush semantics.
> -------------------------------
>
> Key: HDFS-3979
> URL: https://issues.apache.org/jira/browse/HDFS-3979
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node, hdfs client
> Affects Versions: 0.22.0, 0.23.0, 2.0.0-alpha
> Reporter: Lars Hofhansl
> Assignee: Lars Hofhansl
> Attachments: hdfs-3979-sketch.txt, hdfs-3979-v2.txt
>
>
> See discussion in HDFS-744. The actual sync/flush operation in BlockReceiver
> is not on a synchronous path from the DFSClient, hence it is possible that a
> DN loses data that it has already acknowledged as persisted to a client.
> Edit: Spelling.
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