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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-895) Allow hflush/sync to occur in parallel with new writes to the file
Date Tue, 04 May 2010 18:39:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12863935#action_12863935
] 

dhruba borthakur commented on HDFS-895:
---------------------------------------

I like the idea of having a hflush(offset) type of call. It will be non-standard in the sense
that I know of no other filesystems that has such a call, but it would benefit hbase a lot.

> 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: hdfs-895-20.txt, hdfs-895-trunk.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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