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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6782) Improve FS editlog logSync
Date Sun, 03 May 2015 10:46:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6782?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14525764#comment-14525764
] 

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

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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:blue}0{color} | pre-patch |  14m 35s | Pre-patch trunk compilation is healthy. |
| {color:green}+1{color} | @author |   0m  0s | The patch does not contain any @author tags.
|
| {color:red}-1{color} | tests included |   0m  0s | 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{color} | javac |   7m 28s | There were no new javac warning messages. |
| {color:green}+1{color} | javadoc |   9m 32s | There were no new javadoc warning messages.
|
| {color:green}+1{color} | release audit |   0m 23s | The applied patch does not increase
the total number of release audit warnings. |
| {color:green}+1{color} | checkstyle |   2m 13s | There were no new checkstyle issues. |
| {color:red}-1{color} | whitespace |   0m  0s | The patch has 3  line(s) that end in whitespace.
Use git apply --whitespace=fix. |
| {color:green}+1{color} | install |   1m 33s | mvn install still works. |
| {color:green}+1{color} | eclipse:eclipse |   0m 33s | The patch built with eclipse:eclipse.
|
| {color:green}+1{color} | findbugs |   3m  8s | The patch does not introduce any new Findbugs
(version 2.0.3) warnings. |
| {color:green}+1{color} | native |   3m 13s | Pre-build of native portion |
| {color:red}-1{color} | hdfs tests | 165m 17s | Tests failed in hadoop-hdfs. |
| | | 208m  1s | |
\\
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|| Reason || Tests ||
| Failed unit tests | hadoop.hdfs.server.namenode.TestCheckpoint |
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|| Subsystem || Report/Notes ||
| Patch URL | http://issues.apache.org/jira/secure/attachment/12659525/HDFS-6782.002.patch
|
| Optional Tests | javadoc javac unit findbugs checkstyle |
| git revision | trunk / a319771 |
| whitespace | https://builds.apache.org/job/PreCommit-HDFS-Build/10730/artifact/patchprocess/whitespace.txt
|
| hadoop-hdfs test log | https://builds.apache.org/job/PreCommit-HDFS-Build/10730/artifact/patchprocess/testrun_hadoop-hdfs.txt
|
| Test Results | https://builds.apache.org/job/PreCommit-HDFS-Build/10730/testReport/ |
| Java | 1.7.0_55 |
| uname | Linux asf909.gq1.ygridcore.net 3.13.0-36-lowlatency #63-Ubuntu SMP PREEMPT Wed Sep
3 21:56:12 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux |
| Console output | https://builds.apache.org/job/PreCommit-HDFS-Build/10730/console |


This message was 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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