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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 Fri, 12 Nov 2010 19:53:16 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-ontopof-1497.txt

I took out the bug fix for sequence number skip into a patch on HDFS-1497. This new patch,
{{hdfs-895-ontopof-1497.txt}} applies on top of HDFS-1497 and adds the parallel flush capability.
I think we should commit that bug fix first and then add parallel flush - the safety checks
from 1497 make me more confident that we won't accidentally break this tricky code.

> 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
>
>
> 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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