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https://issues.apache.org/jira/browse/HIVE-20983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16928280#comment-16928280
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Hive QA commented on HIVE-20983:
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|| Vote || Subsystem || Runtime || Comment ||
|| || || || {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:brown} master Compile Tests {color} ||
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green}  8m 
39s{color} | {color:green} master passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  1m  
5s{color} | {color:green} master passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  0m 
38s{color} | {color:green} master passed {color} |
| {color:blue}0{color} | {color:blue} findbugs {color} | {color:blue}  3m 
51s{color} | {color:blue} ql in master has 2244 extant Findbugs warnings. 
{color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  0m 
55s{color} | {color:green} master passed {color} |
|| || || || {color:brown} Patch Compile Tests {color} ||
| {color:green}+1{color} | {color:green} mvninstall {color} | {color:green}  1m 
24s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  1m  
1s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green}  1m  
1s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} checkstyle {color} | {color:green}  0m 
37s{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} findbugs {color} | {color:green}  3m 
59s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javadoc {color} | {color:green}  0m 
56s{color} | {color:green} the patch passed {color} |
|| || || || {color:brown} Other Tests {color} ||
| {color:green}+1{color} | {color:green} asflicense {color} | {color:green}  0m 
13s{color} | {color:green} The patch does not generate ASF License warnings. 
{color} |
| {color:black}{color} | {color:black} {color} | {color:black} 23m 48s{color} | 
{color:black} {color} |
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|| Subsystem || Report/Notes ||
| Optional Tests |  asflicense  javac  javadoc  findbugs  checkstyle  compile  |
| uname | Linux hiveptest-server-upstream 3.16.0-4-amd64 #1 SMP Debian 
3.16.43-2+deb8u5 (2017-09-19) x86_64 GNU/Linux |
| Build tool | maven |
| Personality | 
/data/hiveptest/working/yetus_PreCommit-HIVE-Build-18555/dev-support/hive-personality.sh
 |
| git revision | master / 5b1afb7 |
| Default Java | 1.8.0_111 |
| findbugs | v3.0.0 |
| modules | C: ql U: ql |
| Console output | 
http://104.198.109.242/logs//PreCommit-HIVE-Build-18555/yetus.txt |
| Powered by | Apache Yetus    http://yetus.apache.org |


This message was automatically generated.



> Vectorization: Scale up small hashtables, when collisions are detected
> ----------------------------------------------------------------------
>
>                 Key: HIVE-20983
>                 URL: https://issues.apache.org/jira/browse/HIVE-20983
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Gopal V
>            Assignee: Mustafa Iman
>            Priority: Major
>         Attachments: HIVE-20983.1.patch, HIVE-20983.2.patch
>
>
> Hive's hashtable estimates are getting better with HyperLogLog stats in 
> place, but an accurate estimate does not always result in a low number of 
> collisions.
> The hashtables which contain a very small number of items tend to lose their 
> O(1) lookup performance where there are collisions. Since collisions are easy 
> to detect within the fast hashtable implementation, a rehashing to a higher 
> size will help these small hashtables avoid collisions and go back to O(1) 
> perf.



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