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https://issues.apache.org/jira/browse/HBASE-21387?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16695873#comment-16695873
 ] 

Hadoop QA commented on HBASE-21387:
-----------------------------------

| (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 
17s{color} | {color:blue} Docker mode activated. {color} |
|| || || || {color:brown} Prechecks {color} ||
| {color:blue}0{color} | {color:blue} findbugs {color} | {color:blue}  0m  
0s{color} | {color:blue} Findbugs executables are not available. {color} |
| {color:green}+1{color} | {color:green} hbaseanti {color} | {color:green}  0m  
0s{color} | {color:green} Patch does not have any anti-patterns. {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:brown} branch-1.2 Compile Tests {color} ||
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green}  9m 
 4s{color} | {color:green} branch-1.2 passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  0m 
32s{color} | {color:green} branch-1.2 passed with JDK v1.8.0_192 {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  0m 
34s{color} | {color:green} branch-1.2 passed with JDK v1.7.0_201 {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  1m 
18s{color} | {color:green} branch-1.2 passed {color} |
| {color:green}+1{color} | {color:green} shadedjars {color} | {color:green}  2m 
16s{color} | {color:green} branch has no errors when building our shaded 
downstream artifacts. {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  0m 
30s{color} | {color:green} branch-1.2 passed with JDK v1.8.0_192 {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  0m 
31s{color} | {color:green} branch-1.2 passed with JDK v1.7.0_201 {color} |
|| || || || {color:brown} Patch Compile Tests {color} ||
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green}  1m 
23s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  0m 
31s{color} | {color:green} the patch passed with JDK v1.8.0_192 {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green}  0m 
31s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  0m 
34s{color} | {color:green} the patch passed with JDK v1.7.0_201 {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green}  0m 
34s{color} | {color:green} the patch passed {color} |
| {color:red}-1{color} | {color:red} checkstyle {color} | {color:red}  1m 
11s{color} | {color:red} hbase-server: The patch generated 6 new + 242 
unchanged - 2 fixed = 248 total (was 244) {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} shadedjars {color} | {color:green}  2m 
13s{color} | {color:green} patch has no errors when building our shaded 
downstream artifacts. {color} |
| {color:green}+1{color} | {color:green} hadoopcheck {color} | {color:green}  
8m 49s{color} | {color:green} Patch does not cause any errors with Hadoop 2.4.1 
2.5.2 2.6.5 2.7.4. {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  0m 
23s{color} | {color:green} the patch passed with JDK v1.8.0_192 {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  0m 
31s{color} | {color:green} the patch passed with JDK v1.7.0_201 {color} |
|| || || || {color:brown} Other Tests {color} ||
| {color:green}+1{color} | {color:green} unit {color} | {color:green} 75m 
59s{color} | {color:green} hbase-server in the patch passed. {color} |
| {color:green}+1{color} | {color:green} asflicense {color} | {color:green}  0m 
15s{color} | {color:green} The patch does not generate ASF License warnings. 
{color} |
| {color:black}{color} | {color:black} {color} | {color:black}107m 20s{color} | 
{color:black} {color} |
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|| Subsystem || Report/Notes ||
| Docker | Client=17.05.0-ce Server=17.05.0-ce Image:yetus/hbase:34a9b27 |
| JIRA Issue | HBASE-21387 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12949178/HBASE-21387.branch-1.2.patch
 |
| Optional Tests |  dupname  asflicense  javac  javadoc  unit  findbugs  
shadedjars  hadoopcheck  hbaseanti  checkstyle  compile  |
| uname | Linux 9ffddac44f9b 4.4.0-138-generic #164-Ubuntu SMP Tue Oct 2 
17:16:02 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | maven |
| Personality | 
/home/jenkins/jenkins-slave/workspace/PreCommit-HBASE-Build/component/dev-support/hbase-personality.sh
 |
| git revision | branch-1.2 / fd0d55b |
| maven | version: Apache Maven 3.0.5 |
| Default Java | 1.7.0_201 |
| Multi-JDK versions |  /usr/lib/jvm/java-8-openjdk-amd64:1.8.0_192 
/usr/lib/jvm/java-7-openjdk-amd64:1.7.0_201 |
| checkstyle | 
https://builds.apache.org/job/PreCommit-HBASE-Build/15093/artifact/patchprocess/diff-checkstyle-hbase-server.txt
 |
|  Test Results | 
https://builds.apache.org/job/PreCommit-HBASE-Build/15093/testReport/ |
| Max. process+thread count | 4063 (vs. ulimit of 10000) |
| modules | C: hbase-server U: hbase-server |
| Console output | 
https://builds.apache.org/job/PreCommit-HBASE-Build/15093/console |
| Powered by | Apache Yetus 0.8.0   http://yetus.apache.org |


This message was automatically generated.



> Race condition surrounding in progress snapshot handling in snapshot cache 
> leads to loss of snapshot files
> ----------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-21387
>                 URL: https://issues.apache.org/jira/browse/HBASE-21387
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Ted Yu
>            Assignee: Ted Yu
>            Priority: Major
>              Labels: snapshot
>             Fix For: 3.0.0, 1.5.0, 1.3.3, 2.2.0, 2.0.3, 1.4.9, 2.1.2, 1.2.10
>
>         Attachments: 0001-UT.patch, 21387.dbg.txt, 21387.v10.txt, 
> 21387.v11.txt, 21387.v12.txt, 21387.v2.txt, 21387.v3.txt, 21387.v6.txt, 
> 21387.v7.txt, 21387.v8.txt, 21387.v9.txt, HBASE-21387.branch-1.2.patch, 
> HBASE-21387.branch-1.3.patch, HBASE-21387.branch-1.patch, 
> HBASE-21387.v13.patch, HBASE-21387.v14.patch, HBASE-21387.v15.patch, 
> HBASE-21387.v16.patch, HBASE-21387.v17.patch, two-pass-cleaner.v4.txt, 
> two-pass-cleaner.v6.txt, two-pass-cleaner.v9.txt
>
>
> During recent report from customer where ExportSnapshot failed:
> {code}
> 2018-10-09 18:54:32,559 ERROR [VerifySnapshot-pool1-t2] 
> snapshot.SnapshotReferenceUtil: Can't find hfile: 
> 44f6c3c646e84de6a63fe30da4fcb3aa in the real 
> (hdfs://in.com:8020/apps/hbase/data/data/.../a/44f6c3c646e84de6a63fe30da4fcb3aa)
>  or archive 
> (hdfs://in.com:8020/apps/hbase/data/archive/data/.../a/44f6c3c646e84de6a63fe30da4fcb3aa)
>  directory for the primary table. 
> {code}
> We found the following in log:
> {code}
> 2018-10-09 18:54:23,675 DEBUG 
> [00:16000.activeMasterManager-HFileCleaner.large-1539035367427] 
> cleaner.HFileCleaner: Removing: 
> hdfs:///apps/hbase/data/archive/data/.../a/44f6c3c646e84de6a63fe30da4fcb3aa 
> from archive
> {code}
> The root cause is race condition surrounding in progress snapshot(s) handling 
> between refreshCache() and getUnreferencedFiles().
> There are two callers of refreshCache: one from RefreshCacheTask#run and the 
> other from SnapshotHFileCleaner.
> Let's look at the code of refreshCache:
> {code}
>       if (!name.equals(SnapshotDescriptionUtils.SNAPSHOT_TMP_DIR_NAME)) {
> {code}
> whose intention is to exclude in progress snapshot(s).
> Suppose when the RefreshCacheTask runs refreshCache, there is some in 
> progress snapshot (about to finish).
> When SnapshotHFileCleaner calls getUnreferencedFiles(), it sees that 
> lastModifiedTime is up to date. So cleaner proceeds to check in progress 
> snapshot(s). However, the snapshot has completed by that time, resulting in 
> some file(s) deemed unreferenced.
> Here is timeline given by Josh illustrating the scenario:
> At time T0, we are checking if F1 is referenced. At time T1, there is a 
> snapshot S1 in progress that is referencing a file F1. refreshCache() is 
> called, but no completed snapshot references F1. At T2, the snapshot S1, 
> which references F1, completes. At T3, we check in-progress snapshots and S1 
> is not included. Thus, F1 is marked as unreferenced even though S1 references 
> it. 



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