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https://issues.apache.org/jira/browse/HDFS-14211?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16792041#comment-16792041
 ] 

Hadoop QA commented on HDFS-14211:
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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 
12s{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 
29s{color} | {color:blue} Maven dependency ordering for branch {color} |
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green} 18m 
18s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  3m 
31s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  1m 
 2s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  1m 
59s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} shadedclient {color} | {color:green} 
14m 39s{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  
8s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  1m 
24s{color} | {color:green} trunk passed {color} |
|| || || || {color:brown} Patch Compile Tests {color} ||
| {color:blue}0{color} | {color:blue} mvndep {color} | {color:blue}  0m 
11s{color} | {color:blue} Maven dependency ordering for patch {color} |
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green}  1m 
58s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  3m 
45s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green}  3m 
45s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  1m 
 5s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  2m  
5s{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 15s{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 
28s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  1m 
23s{color} | {color:green} the patch passed {color} |
|| || || || {color:brown} Other Tests {color} ||
| {color:green}+1{color} | {color:green} unit {color} | {color:green}  1m 
53s{color} | {color:green} hadoop-hdfs-client in the patch passed. {color} |
| {color:red}-1{color} | {color:red} unit {color} | {color:red} 87m 56s{color} 
| {color:red} hadoop-hdfs in the patch failed. {color} |
| {color:green}+1{color} | {color:green} asflicense {color} | {color:green}  0m 
32s{color} | {color:green} The patch does not generate ASF License warnings. 
{color} |
| {color:black}{color} | {color:black} {color} | {color:black}163m  7s{color} | 
{color:black} {color} |
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|| Reason || Tests ||
| Failed junit tests | 
hadoop.hdfs.server.namenode.ha.TestConsistentReadsObserver |
|   | hadoop.hdfs.web.TestWebHdfsTimeouts |
|   | hadoop.hdfs.TestMaintenanceState |
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|| Subsystem || Report/Notes ||
| Docker | Client=17.05.0-ce Server=17.05.0-ce Image:yetus/hadoop:8f97d6f |
| JIRA Issue | HDFS-14211 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12962365/HDFS-14211.001.patch |
| Optional Tests |  dupname  asflicense  compile  javac  javadoc  mvninstall  
mvnsite  unit  shadedclient  findbugs  checkstyle  |
| uname | Linux 5c3b5a70cb73 4.4.0-138-generic #164~14.04.1-Ubuntu SMP Fri Oct 
5 08:56:16 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | maven |
| Personality | /testptch/patchprocess/precommit/personality/provided.sh |
| git revision | trunk / 1f47fb7 |
| maven | version: Apache Maven 3.3.9 |
| Default Java | 1.8.0_191 |
| findbugs | v3.1.0-RC1 |
| unit | 
https://builds.apache.org/job/PreCommit-HDFS-Build/26468/artifact/out/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt
 |
|  Test Results | 
https://builds.apache.org/job/PreCommit-HDFS-Build/26468/testReport/ |
| Max. process+thread count | 3366 (vs. ulimit of 10000) |
| modules | C: hadoop-hdfs-project/hadoop-hdfs-client 
hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project |
| Console output | 
https://builds.apache.org/job/PreCommit-HDFS-Build/26468/console |
| Powered by | Apache Yetus 0.8.0   http://yetus.apache.org |


This message was automatically generated.



> [Consistent Observer Reads] Allow for configurable "always msync" mode
> ----------------------------------------------------------------------
>
>                 Key: HDFS-14211
>                 URL: https://issues.apache.org/jira/browse/HDFS-14211
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>            Reporter: Erik Krogen
>            Assignee: Erik Krogen
>            Priority: Major
>         Attachments: HDFS-14211.000.patch, HDFS-14211.001.patch
>
>
> To allow for reads to be serviced from an ObserverNode (see HDFS-12943) in a 
> consistent way, an {{msync}} API was introduced (HDFS-13688) to allow for a 
> client to fetch the latest transaction ID from the Active NN, thereby 
> ensuring that subsequent reads from the ObserverNode will be up-to-date with 
> the current state of the Active.
> Using this properly, however, requires application-side changes: for 
> examples, a NodeManager should call {{msync}} before localizing the resources 
> for a client, since it received notification of the existence of those 
> resources via communicate which is out-of-band to HDFS and thus could 
> potentially attempt to localize them prior to the availability of those 
> resources on the ObserverNode.
> Until such application-side changes can be made, which will be a longer-term 
> effort, we need to provide a mechanism for unchanged clients to utilize the 
> ObserverNode without exposing such a client to inconsistencies. This is 
> essentially phase 3 of the roadmap outlined in the [design 
> document|https://issues.apache.org/jira/secure/attachment/12915990/ConsistentReadsFromStandbyNode.pdf]
>  for HDFS-12943.
> The design document proposes some heuristics based on understanding of how 
> common applications (e.g. MR) use HDFS for resources. As an initial pass, we 
> can simply have a flag which tells a client to call {{msync}} before _every 
> single_ read operation. This may seem counterintuitive, as it turns every 
> read operation into two RPCs: {{msync}} to the Active following by an actual 
> read operation to the Observer. However, the {{msync}} operation is extremely 
> lightweight, as it does not acquire the {{FSNamesystemLock}}, and in 
> experiments we have found that this approach can easily scale to well over 
> 100,000 {{msync}} operations per second on the Active (while still servicing 
> approx. 10,000 write op/s). Combined with the fast-path edit log tailing for 
> standby/observer nodes (HDFS-13150), this "always msync" approach should 
> introduce only a few ms of extra latency to each read call.
> Below are some experimental results collected from experiments which convert 
> a normal RPC workload into one in which all read operations are turned into 
> an {{msync}}. The baseline is a workload of 1.5k write op/s and 25k read op/s.
> ||Rate Multiplier|2|4|6|8||
> ||RPC Queue Avg Time (ms)|14|53|110|125||
> ||RPC Queue NumOps Avg (k)|51|102|147|177||
> ||RPC Queue NumOps Max (k)|148|269|306|312||
> _(numbers are approximate and should be viewed primarily for their trends)_
> Results are promising up to between 4x and 6x of the baseline workload, which 
> is approx. 100-150k read op/s.



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