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https://issues.apache.org/jira/browse/HDFS-15240?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17075851#comment-17075851
 ] 

Hadoop QA commented on HDFS-15240:
----------------------------------

| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:blue}0{color} | {color:blue} reexec {color} | {color:blue}  0m 
30s{color} | {color:blue} Docker mode activated. {color} |
|| || || || {color:brown} Prechecks {color} ||
| {color:green}+1{color} | {color:green} @author {color} | {color:green}  0m  
0s{color} | {color:green} The patch does not contain any @author tags. {color} |
| {color:green}+1{color} | {color:green} test4tests {color} | {color:green}  0m 
 0s{color} | {color:green} The patch appears to include 1 new or modified test 
files. {color} |
|| || || || {color:brown} trunk Compile Tests {color} ||
| {color:blue}0{color} | {color:blue} mvndep {color} | {color:blue}  0m 
25s{color} | {color:blue} Maven dependency ordering for branch {color} |
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green} 17m 
44s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green} 15m  
9s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  2m 
37s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  4m  
3s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} shadedclient {color} | {color:green} 
20m 53s{color} | {color:green} branch has no errors when building and testing 
our client artifacts. {color} |
| {color:green}+1{color} | {color:green} findbugs {color} | {color:green}  7m  
6s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  2m 
38s{color} | {color:green} trunk passed {color} |
|| || || || {color:brown} Patch Compile Tests {color} ||
| {color:blue}0{color} | {color:blue} mvndep {color} | {color:blue}  0m 
24s{color} | {color:blue} Maven dependency ordering for patch {color} |
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green}  2m 
27s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green} 14m 
23s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green} 14m 
23s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  2m 
24s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  3m 
38s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} whitespace {color} | {color:green}  0m 
 0s{color} | {color:green} The patch has no whitespace issues. {color} |
| {color:green}+1{color} | {color:green} shadedclient {color} | {color:green} 
13m 19s{color} | {color:green} patch has no errors when building and testing 
our client artifacts. {color} |
| {color:green}+1{color} | {color:green} findbugs {color} | {color:green}  7m 
30s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  2m 
40s{color} | {color:green} the patch passed {color} |
|| || || || {color:brown} Other Tests {color} ||
| {color:green}+1{color} | {color:green} unit {color} | {color:green}  9m  
7s{color} | {color:green} hadoop-common in the patch passed. {color} |
| {color:green}+1{color} | {color:green} unit {color} | {color:green}  2m 
11s{color} | {color:green} hadoop-hdfs-client in the patch passed. {color} |
| {color:red}-1{color} | {color:red} unit {color} | {color:red} 92m 43s{color} 
| {color:red} hadoop-hdfs in the patch passed. {color} |
| {color:green}+1{color} | {color:green} asflicense {color} | {color:green}  0m 
58s{color} | {color:green} The patch does not generate ASF License warnings. 
{color} |
| {color:black}{color} | {color:black} {color} | {color:black}219m 52s{color} | 
{color:black} {color} |
\\
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|| Reason || Tests ||
| Failed junit tests | hadoop.hdfs.server.balancer.TestBalancer |
\\
\\
|| Subsystem || Report/Notes ||
| Docker | Client=19.03.8 Server=19.03.8 Image:yetus/hadoop:e6455cc864d |
| JIRA Issue | HDFS-15240 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12998977/HDFS-15240.005.patch |
| Optional Tests |  dupname  asflicense  compile  javac  javadoc  mvninstall  
mvnsite  unit  shadedclient  findbugs  checkstyle  |
| uname | Linux 040df997653e 4.15.0-58-generic #64-Ubuntu SMP Tue Aug 6 
11:12:41 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | maven |
| Personality | /testptch/patchprocess/precommit/personality/provided.sh |
| git revision | trunk / e6455cc |
| maven | version: Apache Maven 3.3.9 |
| Default Java | 1.8.0_242 |
| findbugs | v3.1.0-RC1 |
| unit | 
https://builds.apache.org/job/PreCommit-HDFS-Build/29084/artifact/out/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt
 |
|  Test Results | 
https://builds.apache.org/job/PreCommit-HDFS-Build/29084/testReport/ |
| Max. process+thread count | 4398 (vs. ulimit of 5500) |
| modules | C: hadoop-common-project/hadoop-common 
hadoop-hdfs-project/hadoop-hdfs-client hadoop-hdfs-project/hadoop-hdfs U: . |
| Console output | 
https://builds.apache.org/job/PreCommit-HDFS-Build/29084/console |
| Powered by | Apache Yetus 0.8.0   http://yetus.apache.org |


This message was automatically generated.



> Erasure Coding: dirty buffer causes reconstruction block error
> --------------------------------------------------------------
>
>                 Key: HDFS-15240
>                 URL: https://issues.apache.org/jira/browse/HDFS-15240
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode, erasure-coding
>            Reporter: HuangTao
>            Assignee: HuangTao
>            Priority: Major
>         Attachments: HDFS-15240.001.patch, HDFS-15240.002.patch, 
> HDFS-15240.003.patch, HDFS-15240.004.patch, HDFS-15240.005.patch
>
>
> When read some lzo files we found some blocks were broken.
> I read back all internal blocks(b0-b8) of the block group(RS-6-3-1024k) from 
> DN directly, and choose 6(b0-b5) blocks to decode other 3(b6', b7', b8') 
> blocks. And find the longest common sequenece(LCS) between b6'(decoded) and 
> b6(read from DN)(b7'/b7 and b8'/b8).
> After selecting 6 blocks of the block group in combinations one time and 
> iterating through all cases, I find one case that the length of LCS is the 
> block length - 64KB, 64KB is just the length of ByteBuffer used by 
> StripedBlockReader. So the corrupt reconstruction block is made by a dirty 
> buffer.
> The following log snippet(only show 2 of 28 cases) is my check program 
> output. In my case, I known the 3th block is corrupt, so need other 5 blocks 
> to decode another 3 blocks, then find the 1th block's LCS substring is block 
> length - 64kb.
> It means (0,1,2,4,5,6)th blocks were used to reconstruct 3th block, and the 
> dirty buffer was used before read the 1th block.
> Must be noted that StripedBlockReader read from the offset 0 of the 1th block 
> after used the dirty buffer.
> {code:java}
> decode from [0, 2, 3, 4, 5, 7] -> [1, 6, 8]
> Check Block(1) first 131072 bytes longest common substring length 4
> Check Block(6) first 131072 bytes longest common substring length 4
> Check Block(8) first 131072 bytes longest common substring length 4
> decode from [0, 2, 3, 4, 5, 6] -> [1, 7, 8]
> Check Block(1) first 131072 bytes longest common substring length 65536
> CHECK AGAIN: Block(1) all 27262976 bytes longest common substring length 
> 27197440  # this one
> Check Block(7) first 131072 bytes longest common substring length 4
> Check Block(8) first 131072 bytes longest common substring length 4{code}
> Now I know the dirty buffer causes reconstruction block error, but how does 
> the dirty buffer come about?
> After digging into the code and DN log, I found this following DN log is the 
> root reason.
> {code:java}
> [INFO] [stripedRead-1017] : Interrupted while waiting for IO on channel 
> java.nio.channels.SocketChannel[connected local=/xxxxxxxx:52586 
> remote=/xxxxxxxx:50010]. 180000 millis timeout left.
> [WARN] [StripedBlockReconstruction-199] : Failed to reconstruct striped 
> block: BP-714356632-xxxxxxxx-1519726836856:blk_-YYYYYYYYYYYYYY_3472979393
> java.lang.NullPointerException
>     at 
> org.apache.hadoop.hdfs.util.StripedBlockUtil.getNextCompletedStripedRead(StripedBlockUtil.java:314)
>     at 
> org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedReader.doReadMinimumSources(StripedReader.java:308)
>     at 
> org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedReader.readMinimumSources(StripedReader.java:269)
>     at 
> org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedBlockReconstructor.reconstruct(StripedBlockReconstructor.java:94)
>     at 
> org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedBlockReconstructor.run(StripedBlockReconstructor.java:60)
>     at 
> java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
>     at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
>     at 
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
>     at 
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
>     at java.base/java.lang.Thread.run(Thread.java:834) {code}
> Reading from DN may timeout(hold by a future(F)) and output the INFO log, but 
> the futures that contains the future(F)  is cleared, 
> {code:java}
> return new StripingChunkReadResult(futures.remove(future),
>     StripingChunkReadResult.CANCELLED); {code}
> futures.remove(future) cause NPE. So the EC reconstruction is failed. In the 
> finally phase, the code snippet in *getStripedReader().close()* 
> {code:java}
> reconstructor.freeBuffer(reader.getReadBuffer());
> reader.freeReadBuffer();
> reader.closeBlockReader(); {code}
> free buffer firstly, but the StripedBlockReader still holds the buffer and 
> write it.



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