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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HDFS-895) Allow hflush/sync to occur in parallel with new writes to the file
Date Thu, 02 Dec 2010 23:38:15 GMT

     [ https://issues.apache.org/jira/browse/HDFS-895?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon updated HDFS-895:
-----------------------------

    Attachment: hdfs-895-0.20-append.txt

Stack requested a patch for 0.20-append. This one ought to work, but I haven't done testing
aside from running the new unit test. It's based on the patch from CDH3 which has been deployed
and tested at scale, but slightly modified based on the more recent changes to the trunk version.

> 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-895-0.20-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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