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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-895) Allow hflush/sync to occur in parallel with new writes to the file
Date Mon, 15 Nov 2010 20:48:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12932189#action_12932189
] 

Todd Lipcon commented on HDFS-895:
----------------------------------

Yes, we should get this into 20-append for HBase. Right now there seems to be an issue with
the HDFS-724 patch in 20-append, and since these touch very similar areas of the write pipeline,
I want to either temporarily revert 724 from 20-append, or figure out what's wrong with it.
No sense adding another variable into the mix when our current branch has some problems.

> Allow hflush/sync to occur in parallel with new writes to the file
> ------------------------------------------------------------------
>
>                 Key: HDFS-895
>                 URL: https://issues.apache.org/jira/browse/HDFS-895
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>    Affects Versions: 0.22.0
>            Reporter: dhruba borthakur
>            Assignee: Todd Lipcon
>             Fix For: 0.22.0
>
>         Attachments: 895-delta-for-review.txt, hdfs-895-0.20-append.txt, hdfs-895-20.txt,
hdfs-895-branch-20-append.txt, hdfs-895-ontopof-1497.txt, hdfs-895-review.txt, hdfs-895-trunk.txt,
hdfs-895.txt, hdfs-895.txt, hdfs-895.txt, hdfs-895.txt, hdfs-895.txt, hdfs-895.txt, hdfs-895.txt
>
>
> In the current trunk, the HDFS client methods writeChunk() and hflush./sync are syncronized.
This means that if a hflush/sync is in progress, an applicationn cannot write data to the
HDFS client buffer. This reduces the write throughput of the transaction log in HBase. 
> The hflush/sync should allow new writes to happen to the HDFS client even when a hflush/sync
is in progress. It can record the seqno of the message for which it should receice the ack,
indicate to the DataStream thread to star flushing those messages, exit the synchronized section
 and just wai for that ack to arrive.

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