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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 Mon, 15 Nov 2010 15:53:18 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.txt

I ran the unit tests and caught one more bug that caused TestFiPipelineClose to fail. The
issue was that if faliure recovery happens in PIPELINE_CLOSE stage, the "last packet in block"
packet gets removed from dataQueue after the close() caller is already waiting for that sequence
number. Thus the sequence number never comes and the caller of close() hangs. The fix is to
set lastAckedSeqNo to the lastPacketInBlock seqno when it is removed from dataQueue. I also
added some asserts in this code path.

> 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, 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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