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https://issues.apache.org/jira/browse/HIVE-15023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15591060#comment-15591060
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Jesus Camacho Rodriguez commented on HIVE-15023:
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[~pxiong], this indeed solves some of the issues referred in HIVE-14866. I
wrongly thought that one of the problems was that we were not setting the
_outerQueryLimit_ variable for simple queries in SemanticAnalyzer, but we do;
thanks for discovering that.
To understand properly the fix: _outerQueryLimit=0_ was previously checked in
TaskCompiler (L200), but apparently if SimpleFetchOptimizer kicks in, we never
reach that line (we enter in L119-L137), thus you are proposing to bail out
from SimpleFetchOptimizer if limit is 0, is that right? I think another
possibility is to move the check in TaskCompiler in L200 and have it before
L119; the advantage with this approach would be that we avoid dealing with the
special case _limit=0_ in both places. What do you think? Would that work?
> SimpleFetchOptimizer needs to optimize limit=0
> ----------------------------------------------
>
> Key: HIVE-15023
> URL: https://issues.apache.org/jira/browse/HIVE-15023
> Project: Hive
> Issue Type: Sub-task
> Reporter: Pengcheng Xiong
> Assignee: Pengcheng Xiong
> Attachments: HIVE-15023.01.patch
>
>
> on current master
> {code}
> hive> explain select key from src limit 0;
> OK
> STAGE DEPENDENCIES:
> Stage-0 is a root stage
> STAGE PLANS:
> Stage: Stage-0
> Fetch Operator
> limit: 0
> Processor Tree:
> TableScan
> alias: src
> Statistics: Num rows: 500 Data size: 5312 Basic stats: COMPLETE
> Column stats: NONE
> Select Operator
> expressions: key (type: string)
> outputColumnNames: _col0
> Statistics: Num rows: 500 Data size: 5312 Basic stats: COMPLETE
> Column stats: NONE
> Limit
> Number of rows: 0
> Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
> stats: NONE
> ListSink
> Time taken: 7.534 seconds, Fetched: 20 row(s)
> {code}
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