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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6782) Improve FS editlog logSync
Date Sun, 03 Aug 2014 07:56:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6782?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14083903#comment-14083903
] 

Hadoop QA commented on HDFS-6782:
---------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12659525/HDFS-6782.002.patch
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:red}-1 tests included{color}.  The patch doesn't appear to include any new or modified
tests.
                        Please justify why no new tests are needed for this patch.
                        Also please list what manual steps were performed to verify this patch.

    {color:green}+1 javac{color}.  The applied patch does not increase the total number of
javac compiler warnings.

    {color:green}+1 javadoc{color}.  There were no new javadoc warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new Findbugs (version
2.0.3) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:green}+1 core tests{color}.  The patch passed unit tests in hadoop-hdfs-project/hadoop-hdfs.

    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/7545//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/7545//console

This message is automatically generated.

> Improve FS editlog logSync
> --------------------------
>
>                 Key: HDFS-6782
>                 URL: https://issues.apache.org/jira/browse/HDFS-6782
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.4.1
>            Reporter: Yi Liu
>            Assignee: Yi Liu
>         Attachments: HDFS-6782.001.patch, HDFS-6782.002.patch
>
>
> In NN, it uses a double buffer (bufCurrent, bufReady) for log sync, bufCurrent it to
buffer new coming edit ops and bufReady is for flushing. This's efficient. When flush is ongoing,
and bufCurrent is full, NN goes to force log sync, and all new Ops are blocked (since force
log sync is protected by FSNameSystem write lock). After the flush finished, the new Ops are
still blocked, but actually at this time, bufCurrent is free and Ops can go ahead and write
to the buffer. The following diagram shows the detail. This JIRA is for this improvement.
 Thanks [~umamaheswararao] for confirming this issue.
> {code}
> edit1(txid1) ------ write to bufCurrent -------- logSync --------- (swap buffer)flushing
-------
> edit2(txid2) ------ write to bufCurrent -------- logSync --------- waiting -------
> edit3(txid3) ------ write to bufCurrent -------- logSync --------- waiting -------
> edit4(txid4) ------ write to bufCurrent -------- logSync --------- waiting -------
> edit5(txid5) ------ write to bufCurrent --full-- force sync --------- waiting -------
> edit6(txid6) ------ blocked
> ...
> editn(txidn) ------ blocked
> {code}
> After the flush, it becomes
> {code}
> edit1(txid1) ------ write to bufCurrent -------- logSync --------- finished --------
> edit2(txid2) ------ write to bufCurrent -------- logSync --------- flushing -------
> edit3(txid3) ------ write to bufCurrent -------- logSync --------- waiting -------
> edit4(txid4) ------ write to bufCurrent -------- logSync --------- waiting -------
> edit5(txid5) ------ write to bufCurrent --full-- force sync --------- waiting -------
> edit6(txid6) ------ blocked
> ...
> editn(txidn) ------ blocked
> {code}
> After edit1 finished, bufCurrent is free, and the thread which flushes txid2 will also
flushes txid3-5, so we should return from the force sync of edit5 and FSNamesystem write lock
will be freed (Don't worry that edit5 Op will return, since there will be a normal logSync
after the force logSync and there will wait for sync finished). This is the idea of this JIRA.




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