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From "Kan Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3979) Fix hsync and hflush semantics.
Date Sat, 06 Oct 2012 00:42:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13470823#comment-13470823

Kan Zhang commented on HDFS-3979:

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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