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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 Mon, 08 Nov 2010 07:52:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12929485#action_12929485
] 

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

The patch looks good. A few questions:
1. Does this work with the heartbeat packet?
2. line 1387: dataQueue.wait(1000); is it possible to use dataQueue.wait();
3. lines 1294-1299:        when would this happen?
         if (oldCurrentPacket == null && currentPacket != null) {
            // If we didn't previously have a packet queued, and now we do,
            // but we don't plan on sending it, then we should not
            // skip a sequence number for it!
            currentSeqno--;
          }

> 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-895-0.20-append.txt, hdfs-895-20.txt, hdfs-895-review.txt,
hdfs-895-trunk.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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