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Posted to issues@kylin.apache.org by "XiaoXiang Yu (JIRA)" <ji...@apache.org> on 2018/12/16 09:26:00 UTC
[jira] [Commented] (KYLIN-3722) Error Limit Push Down
[ https://issues.apache.org/jira/browse/KYLIN-3722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16722431#comment-16722431 ]
XiaoXiang Yu commented on KYLIN-3722:
-------------------------------------
!image-2018-12-16-17-24-21-017.png!
> Error Limit Push Down
> ---------------------
>
> Key: KYLIN-3722
> URL: https://issues.apache.org/jira/browse/KYLIN-3722
> Project: Kylin
> Issue Type: Bug
> Components: Query Engine
> Affects Versions: all
> Reporter: XiaoXiang Yu
> Assignee: XiaoXiang Yu
> Priority: Major
> Labels: LimitPushDown
> Fix For: v2.6.0
>
> Attachments: image-2018-12-16-17-06-16-341.png, image-2018-12-16-17-24-21-017.png
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> +*Kylin limit-pushdown is sometimes cause data reduction.*+
> For example:
> {quote}select uid, sum(active_minutes) as am
> from useraction
> where item_id in (
> select distinct item_id
> from iteminfo
> where item_type in ('Video')
> ) and act_type != 'share'
> group by uid
> limit 10
> {quote}
> +*In hive, we got correct result(Five row).*+
> {quote}hive>
> > select uid, sum(active_minutes) as am
> > from useraction
> > where item_id in (
> > select distinct item_id
> > from iteminfo
> > where item_type in ('Video')
> > ) and act_type != 'share'
> > group by uid
> > limit 10;
> Query ID = root_20181216170145_d5667a81-46d0-4899-a4bb-7c580155049e
> Total jobs = 1
> Launching Job 1 out of 1
> Status: Running (Executing on YARN cluster with App id application_1539833412107_0414)
> --------------------------------------------------------------------------------
> VERTICES STATUS TOTAL COMPLETED RUNNING PENDING FAILED KILLED
> --------------------------------------------------------------------------------
> Map 1 .......... SUCCEEDED 1 1 0 0 0 0
> Map 3 .......... SUCCEEDED 1 1 0 0 0 0
> Reducer 2 ...... SUCCEEDED 1 1 0 0 0 0
> Reducer 4 ...... SUCCEEDED 1 1 0 0 0 0
> --------------------------------------------------------------------------------
> VERTICES: 04/04 [==========================>>] 100% ELAPSED TIME: 7.67 s
> --------------------------------------------------------------------------------
> OK
> 1 14565.470000000008
> 2 64744.89000000003
> 3 64939.01999999984
> 5 36563.76999999997
> 6 36641.64999999999
> Time taken: 11.02 seconds, Fetched: 5 row(s)
> {quote}
> +*In Kylin, same query got error result(only THREE row). But when you set limit to 50000(original value). It is OK.*+
> !image-2018-12-16-17-06-16-341.png!
> This error is reported by Meituan's Dev.
>
> We can find following things in log：
> {quote}
> KYLIN [ DEBUG ] 12-16 17:04:28.299 org.apache.kylin.storage.gtrecord.GTCubeStorageQueryBase.enableStorageLimitIfPossible(GTCubeStorageQueryBase.java:433) from Query 78808744-8324-3ad4-58ac-93ad7cd8a708-81
> > storageLimitLevel set to LIMIT_ON_RETURN_SIZE because groupD is not clustered at head, groupsD: \{0} with cuboid columns: \{1}
> KYLIN [ INFO ] 12-16 17:04:28.299 org.apache.kylin.storage.StorageContext.applyLimitPushDown(StorageContext.java:167) from Query 78808744-8324-3ad4-58ac-93ad7cd8a708-81
> > Enabling limit push down: 10 at level: LIMIT_ON_RETURN_SIZE
> {quote}
>
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