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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-895) Allow hflush/sync to occur in parallel with new writes to the file
Date Fri, 12 Nov 2010 18:35:18 GMT

    [ https://issues.apache.org/jira/browse/HDFS-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12931483#action_12931483
] 

Hairong Kuang commented on HDFS-895:
------------------------------------

> Would it be better to open a very small JIRA to add the assert and fix for it, commit
that, then commit this as an optimization? That would keep the two changes orthogonal and
maybe easier to understand?

The assertion is a nice thing to have. Please open a jira for adding this assertion. The ideal
fix is not to create the packet.  Let's focus this jira on parallel hflush, which is what
hbase really needs.

> 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-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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