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https://issues.apache.org/jira/browse/HDFS-15150?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17031875#comment-17031875
 ] 

Hadoop QA commented on HDFS-15150:
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| (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 
56s{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 8 new or modified test 
files. {color} |
|| || || || {color:brown} trunk Compile Tests {color} ||
| {color:blue}0{color} | {color:blue} mvndep {color} | {color:blue}  0m 
24s{color} | {color:blue} Maven dependency ordering for branch {color} |
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green} 21m 
 9s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green} 16m 
46s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  2m 
55s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  2m 
51s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} shadedclient {color} | {color:green} 
20m 28s{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}  4m 
24s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  2m 
45s{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}  1m 
55s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green} 16m  
4s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green} 16m  
4s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  2m 
59s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  2m 
51s{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} xml {color} | {color:green}  0m  
2s{color} | {color:green} The patch has no ill-formed XML file. {color} |
| {color:green}+1{color} | {color:green} shadedclient {color} | {color:green} 
13m 34s{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}  4m 
19s{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}  8m 
55s{color} | {color:green} hadoop-common in the patch passed. {color} |
| {color:red}-1{color} | {color:red} unit {color} | {color:red}107m 13s{color} 
| {color:red} hadoop-hdfs in the patch failed. {color} |
| {color:green}+1{color} | {color:green} asflicense {color} | {color:green}  0m 
47s{color} | {color:green} The patch does not generate ASF License warnings. 
{color} |
| {color:black}{color} | {color:black} {color} | {color:black}231m 46s{color} | 
{color:black} {color} |
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|| Reason || Tests ||
| Failed junit tests | hadoop.hdfs.TestDistributedFileSystem |
|   | hadoop.hdfs.server.datanode.TestNNHandlesBlockReportPerStorage |
|   | hadoop.hdfs.qjournal.server.TestJournalNodeSync |
|   | hadoop.hdfs.server.namenode.ha.TestDelegationTokensWithHA |
|   | hadoop.hdfs.TestRollingUpgrade |
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|| Subsystem || Report/Notes ||
| Docker | Client=19.03.5 Server=19.03.5 Image:yetus/hadoop:c44943d1fc3 |
| JIRA Issue | HDFS-15150 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12992783/HDFS-15150.003.patch |
| Optional Tests |  dupname  asflicense  compile  javac  javadoc  mvninstall  
mvnsite  unit  shadedclient  findbugs  checkstyle  xml  |
| uname | Linux 67c5ea5f7fef 4.15.0-74-generic #84-Ubuntu SMP Thu Dec 19 
08:06:28 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | maven |
| Personality | /testptch/patchprocess/precommit/personality/provided.sh |
| git revision | trunk / 146ca0f |
| maven | version: Apache Maven 3.3.9 |
| Default Java | 1.8.0_232 |
| findbugs | v3.1.0-RC1 |
| unit | 
https://builds.apache.org/job/PreCommit-HDFS-Build/28745/artifact/out/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt
 |
|  Test Results | 
https://builds.apache.org/job/PreCommit-HDFS-Build/28745/testReport/ |
| Max. process+thread count | 2876 (vs. ulimit of 5500) |
| modules | C: hadoop-common-project/hadoop-common 
hadoop-hdfs-project/hadoop-hdfs U: . |
| Console output | 
https://builds.apache.org/job/PreCommit-HDFS-Build/28745/console |
| Powered by | Apache Yetus 0.8.0   http://yetus.apache.org |


This message was automatically generated.



> Introduce read write lock to Datanode
> -------------------------------------
>
>                 Key: HDFS-15150
>                 URL: https://issues.apache.org/jira/browse/HDFS-15150
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 3.3.0
>            Reporter: Stephen O'Donnell
>            Assignee: Stephen O'Donnell
>            Priority: Major
>         Attachments: HDFS-15150.001.patch, HDFS-15150.002.patch, 
> HDFS-15150.003.patch
>
>
> HDFS-9668 pointed out the issues around the DN lock being a point of 
> contention some time ago, but that Jira went in a direction of creating a new 
> FSDataset implementation which is very risky, and activity on the Jira has 
> stalled for a few years now. Edit: Looks like HDFS-9668 eventually went in a 
> similar direction to what I was thinking, so I will review that Jira in more 
> detail to see if this one is necessary.
> I feel there could be significant gains by moving to a ReentrantReadWrite 
> lock within the DN. The current implementation is simply a ReentrantLock so 
> any locker blocks all others.
> Once place I think a read lock would benefit us significantly, is when the DN 
> is serving a lot of small blocks and there are jobs which perform a lot of 
> reads. The start of reading any blocks right now takes the lock, but if we 
> moved this to a read lock, many reads could do this at the same time.
> The first conservative step, would be to change the current lock and then 
> make all accesses to it obtain the write lock. That way, we should keep the 
> current behaviour and then we can selectively move some lock accesses to the 
> readlock in separate Jiras.
> I would appreciate any thoughts on this, and also if anyone has attempted it 
> before and found any blockers.



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