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https://issues.apache.org/jira/browse/HBASE-17655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15885725#comment-15885725
 ] 

Hadoop QA commented on HBASE-17655:
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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 14s 
{color} | {color:blue} Docker mode activated. {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 9 new or modified test 
files. {color} |
| {color:blue}0{color} | {color:blue} mvndep {color} | {color:blue} 0m 12s 
{color} | {color:blue} Maven dependency ordering for branch {color} |
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green} 3m 
31s {color} | {color:green} master passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green} 0m 57s 
{color} | {color:green} master passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green} 1m 
41s {color} | {color:green} master passed {color} |
| {color:green}+1{color} | {color:green} mvneclipse {color} | {color:green} 0m 
32s {color} | {color:green} master passed {color} |
| {color:green}+1{color} | {color:green} findbugs {color} | {color:green} 2m 
27s {color} | {color:green} master passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green} 0m 41s 
{color} | {color:green} master passed {color} |
| {color:blue}0{color} | {color:blue} mvndep {color} | {color:blue} 0m 12s 
{color} | {color:blue} Maven dependency ordering for patch {color} |
| {color:red}-1{color} | {color:red} mvninstall {color} | {color:red} 0m 36s 
{color} | {color:red} hbase-server in the patch failed. {color} |
| {color:red}-1{color} | {color:red} mvninstall {color} | {color:red} 0m 13s 
{color} | {color:red} hbase-examples in the patch failed. {color} |
| {color:red}-1{color} | {color:red} compile {color} | {color:red} 0m 37s 
{color} | {color:red} hbase-server in the patch failed. {color} |
| {color:red}-1{color} | {color:red} compile {color} | {color:red} 0m 14s 
{color} | {color:red} hbase-examples in the patch failed. {color} |
| {color:red}-1{color} | {color:red} javac {color} | {color:red} 0m 37s {color} 
| {color:red} hbase-server in the patch failed. {color} |
| {color:red}-1{color} | {color:red} javac {color} | {color:red} 0m 14s {color} 
| {color:red} hbase-examples in the patch failed. {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green} 1m 
39s {color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} mvneclipse {color} | {color:green} 0m 
30s {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:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 1m 24s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.6.1. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 2m 47s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.6.2. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 4m 16s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.6.3. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 5m 47s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.6.4. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 7m 12s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.6.5. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 8m 35s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.7.1. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 9m 59s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.7.2. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 11m 23s 
{color} | {color:red} The patch causes 28 errors with Hadoop v2.7.3. {color} |
| {color:red}-1{color} | {color:red} hadoopcheck {color} | {color:red} 12m 52s 
{color} | {color:red} The patch causes 28 errors with Hadoop v3.0.0-alpha2. 
{color} |
| {color:red}-1{color} | {color:red} findbugs {color} | {color:red} 0m 34s 
{color} | {color:red} hbase-server in the patch failed. {color} |
| {color:red}-1{color} | {color:red} findbugs {color} | {color:red} 0m 16s 
{color} | {color:red} hbase-examples in the patch failed. {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green} 0m 51s 
{color} | {color:green} the patch passed {color} |
| {color:red}-1{color} | {color:red} unit {color} | {color:red} 0m 48s {color} 
| {color:red} hbase-server in the patch failed. {color} |
| {color:red}-1{color} | {color:red} unit {color} | {color:red} 0m 17s {color} 
| {color:red} hbase-examples in the patch failed. {color} |
| {color:green}+1{color} | {color:green} asflicense {color} | {color:green} 0m 
17s {color} | {color:green} The patch does not generate ASF License warnings. 
{color} |
| {color:black}{color} | {color:black} {color} | {color:black} 30m 45s {color} 
| {color:black} {color} |
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|| Subsystem || Report/Notes ||
| Docker | Client=1.11.2 Server=1.11.2 Image:yetus/hbase:8d52d23 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12854885/HBASE-17655-V02.patch 
|
| JIRA Issue | HBASE-17655 |
| Optional Tests |  asflicense  javac  javadoc  unit  findbugs  hadoopcheck  
hbaseanti  checkstyle  compile  |
| uname | Linux 63d8f9f2672c 3.13.0-105-generic #152-Ubuntu SMP Fri Dec 2 
15:37:11 UTC 2016 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 | master / 4d90425 |
| Default Java | 1.8.0_121 |
| findbugs | v3.0.0 |
| mvninstall | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-mvninstall-hbase-server.txt
 |
| mvninstall | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-mvninstall-hbase-examples.txt
 |
| compile | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-compile-hbase-server.txt
 |
| compile | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-compile-hbase-examples.txt
 |
| javac | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-compile-hbase-server.txt
 |
| javac | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-compile-hbase-examples.txt
 |
| findbugs | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-findbugs-hbase-server.txt
 |
| findbugs | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-findbugs-hbase-examples.txt
 |
| unit | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-unit-hbase-server.txt
 |
| unit | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/artifact/patchprocess/patch-unit-hbase-examples.txt
 |
|  Test Results | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/testReport/ |
| modules | C: hbase-server hbase-examples U: . |
| Console output | 
https://builds.apache.org/job/PreCommit-HBASE-Build/5856/console |
| Powered by | Apache Yetus 0.3.0   http://yetus.apache.org |


This message was automatically generated.



> Removing MemStoreScanner and SnapshotScanner
> --------------------------------------------
>
>                 Key: HBASE-17655
>                 URL: https://issues.apache.org/jira/browse/HBASE-17655
>             Project: HBase
>          Issue Type: Improvement
>          Components: Scanners
>    Affects Versions: 2.0.0
>            Reporter: Eshcar Hillel
>            Assignee: Eshcar Hillel
>         Attachments: HBASE-17655-V01.patch, HBASE-17655-V02.patch
>
>
> With CompactingMemstore becoming the new default, a store comprises multiple 
> memory segments and not just 1-2. MemStoreScanner encapsulates the scanning 
> of segments in the memory part of the store. SnapshotScanner is used to scan 
> the snapshot segment upon flush to disk.
> Having the logic of scanners scattered in multiple classes (StoreScanner, 
> SegmentScanner, MemStoreScanner, SnapshotScanner) makes maintainance and 
> debugging challenging tasks, not always for a good reason.
> For example, MemStoreScanner has a KeyValueHeap (KVH). When creating the 
> store scanner which also has a KVH, this makes a KVH inside a KVH. Reasoning 
> about the correctness of the methods supported by the scanner (seek, next, 
> hasNext, peek, etc.) is hard and debugging  them is cumbersome. 
> In addition, by removing the MemStoreScanner layer we allow store scanner to 
> filter out each one of the memory scanners instead of either taking them all 
> (in most cases) or discarding them all (rarely).
> SnapshotScanner is a simplified version of SegmentScanner as it is used only 
> in a specific context. However it is an additional implementation of the same 
> logic with no real advantage of improved performance.
> Therefore, I suggest removing both MemStoreScanner and SnapshotScanner. The 
> code is adjusted to handle the list of segment scanners they encapsulate.
> This fits well with the current code since in most cases at some point a list 
> of scanner is expected, so passing the actual list of segment scanners is 
> more natural than wrapping a single (high level) scanner with 
> Collections.singeltonList(...).



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