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https://issues.apache.org/jira/browse/HDFS-11402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15977924#comment-15977924
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Hadoop QA commented on HDFS-11402:
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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 
35s{color} | {color:blue} Docker mode activated. {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 4 new or modified test 
files. {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} 15m 
40s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  1m 
27s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  0m 
48s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  1m 
26s{color} | {color:green} trunk passed {color} |
| {color:green}+1{color} | {color:green} mvneclipse {color} | {color:green}  0m 
28s{color} | {color:green} trunk passed {color} |
| {color:red}-1{color} | {color:red} findbugs {color} | {color:red}  1m 
22s{color} | {color:red} hadoop-hdfs-project/hadoop-hdfs-client in trunk has 2 
extant Findbugs warnings. {color} |
| {color:red}-1{color} | {color:red} findbugs {color} | {color:red}  1m 
40s{color} | {color:red} hadoop-hdfs-project/hadoop-hdfs in trunk has 10 extant 
Findbugs warnings. {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  1m  
4s{color} | {color:green} trunk passed {color} |
| {color:blue}0{color} | {color:blue} mvndep {color} | {color:blue}  0m  
8s{color} | {color:blue} Maven dependency ordering for patch {color} |
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green}  1m 
33s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  1m 
26s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green}  1m 
26s{color} | {color:green} the patch passed {color} |
| {color:orange}-0{color} | {color:orange} checkstyle {color} | {color:orange}  
0m 50s{color} | {color:orange} hadoop-hdfs-project: The patch generated 2 new + 
788 unchanged - 4 fixed = 790 total (was 792) {color} |
| {color:green}+1{color} | {color:green} mvnsite {color} | {color:green}  1m 
27s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} mvneclipse {color} | {color:green}  0m 
27s{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} findbugs {color} | {color:green}  3m 
39s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  1m  
8s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} unit {color} | {color:green}  1m 
20s{color} | {color:green} hadoop-hdfs-client in the patch passed. {color} |
| {color:green}+1{color} | {color:green} unit {color} | {color:green} 94m  
4s{color} | {color:green} hadoop-hdfs in the patch passed. {color} |
| {color:green}+1{color} | {color:green} asflicense {color} | {color:green}  0m 
20s{color} | {color:green} The patch does not generate ASF License warnings. 
{color} |
| {color:black}{color} | {color:black} {color} | {color:black}133m  6s{color} | 
{color:black} {color} |
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|| Subsystem || Report/Notes ||
| Docker |  Image:yetus/hadoop:0ac17dc |
| JIRA Issue | HDFS-11402 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12864389/HDFS-11402.06.patch |
| Optional Tests |  asflicense  compile  javac  javadoc  mvninstall  mvnsite  
unit  findbugs  checkstyle  xml  |
| uname | Linux d142ce37debf 3.13.0-108-generic #155-Ubuntu SMP Wed Jan 11 
16:58:52 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | maven |
| Personality | /testptch/hadoop/patchprocess/precommit/personality/provided.sh 
|
| git revision | trunk / f356f0f |
| Default Java | 1.8.0_121 |
| findbugs | v3.1.0-RC1 |
| findbugs | 
https://builds.apache.org/job/PreCommit-HDFS-Build/19165/artifact/patchprocess/branch-findbugs-hadoop-hdfs-project_hadoop-hdfs-client-warnings.html
 |
| findbugs | 
https://builds.apache.org/job/PreCommit-HDFS-Build/19165/artifact/patchprocess/branch-findbugs-hadoop-hdfs-project_hadoop-hdfs-warnings.html
 |
| checkstyle | 
https://builds.apache.org/job/PreCommit-HDFS-Build/19165/artifact/patchprocess/diff-checkstyle-hadoop-hdfs-project.txt
 |
|  Test Results | 
https://builds.apache.org/job/PreCommit-HDFS-Build/19165/testReport/ |
| 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/19165/console |
| Powered by | Apache Yetus 0.5.0-SNAPSHOT   http://yetus.apache.org |


This message was automatically generated.



> HDFS Snapshots should capture point-in-time copies of OPEN files
> ----------------------------------------------------------------
>
>                 Key: HDFS-11402
>                 URL: https://issues.apache.org/jira/browse/HDFS-11402
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs
>    Affects Versions: 2.6.0
>            Reporter: Manoj Govindassamy
>            Assignee: Manoj Govindassamy
>         Attachments: HDFS-11402.01.patch, HDFS-11402.02.patch, 
> HDFS-11402.03.patch, HDFS-11402.04.patch, HDFS-11402.05.patch, 
> HDFS-11402.06.patch
>
>
> *Problem:*
> 1. When there are files being written and when HDFS Snapshots are taken in 
> parallel, Snapshots do capture all these files, but these being written files 
> in Snapshots do not have the point-in-time file length captured. That is, 
> these open files are not frozen in HDFS Snapshots. These open files 
> grow/shrink in length, just like the original file, even after the snapshot 
> time.
> 2. At the time of File close or any other meta data modification operation on 
> these files, HDFS reconciles the file length and records the modification in 
> the last taken Snapshot. All the previously taken Snapshots continue to have 
> those open Files with no modification recorded. So, all those previous 
> snapshots end up using the final modification record in the last snapshot. 
> Thus after the file close, file lengths in all those snapshots will end up 
> same.
> Assume File1 is opened for write and a total of 1MB written to it. While the 
> writes are happening, snapshots are taken in parallel.
> {noformat}
> |---Time---T1-----------T2-------------T3----------------T4------>
> |-----------------------Snap1----------Snap2-------------Snap3--->
> |---File1.open---write---------write-----------close------------->
> {noformat}
> Then at time,
> T2:
> Snap1.File1.length = 0
> T3:
> Snap1.File1.length = 0
> Snap2.File1.length = 0
> <File1 write completed and closed>
> T4:
> Snap1.File1.length = 1MB
> Snap2.File1.length = 1MB
> Snap3.File1.length = 1MB
> *Proposal*
> 1. At the time of taking Snapshot, {{SnapshotManager#createSnapshot}} can 
> optionally request {{DirectorySnapshottableFeature#addSnapshot}} to freeze 
> open files. 
> 2. {{DirectorySnapshottableFeature#addSnapshot}} can consult with 
> {{LeaseManager}} and get a list INodesInPath for all open files under the 
> snapshot dir. 
> 3. {{DirectorySnapshottableFeature#addSnapshot}} after the Snapshot creation, 
> Diff creation and updating modification time, can invoke 
> {{INodeFile#recordModification}} for each of the open files. This way, the 
> Snapshot just taken will have a {{FileDiff}} with {{fileSize}} captured for 
> each of the open files. 
> 4. Above model follows the current Snapshot and Diff protocols and doesn't 
> introduce any any disk formats. So, I don't think we will be needing any new 
> FSImage Loader/Saver changes for Snapshots.
> 5. One of the design goals of HDFS Snapshot was ability to take any number of 
> snapshots in O(1) time. LeaseManager though has all the open files with 
> leases in-memory map, an iteration is still needed to prune the needed open 
> files and then run recordModification on each of them. So, it will not be a 
> strict O(1) with the above proposal. But, its going be a marginal increase 
> only as the new order will be of O(open_files_under_snap_dir). In order to 
> avoid HDFS Snapshots change in behavior for open files and avoid change in 
> time complexity, this improvement can be made under a new config 
> {{"dfs.namenode.snapshot.freeze.openfiles"}} which by default can be 
> {{false}}.



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