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https://issues.apache.org/jira/browse/HIVE-24579?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17414151#comment-17414151
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Nemon Lou commented on HIVE-24579:
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I think topn key operator has the same issue. What's your Opinion? [~kkasa]
> Incorrect Result For Groupby With Limit
> ---------------------------------------
>
> Key: HIVE-24579
> URL: https://issues.apache.org/jira/browse/HIVE-24579
> Project: Hive
> Issue Type: Bug
> Affects Versions: 2.3.7, 3.1.2, 4.0.0
> Reporter: Nemon Lou
> Priority: Major
>
> {code:sql}
> create table test(id int);
> explain extended select id,count(*) from test group by id limit 10;
> {code}
> There is an TopN unexpectly for map phase, which casues incorrect result.
> {code:sql}
> STAGE PLANS:
> Stage: Stage-1
> Tez
> DagId: root_20210104141527_c599c0cd-ca2f-4c7d-a3cc-3a01d65c49a1:5
> Edges:
> Reducer 2 <- Map 1 (SIMPLE_EDGE)
> DagName: root_20210104141527_c599c0cd-ca2f-4c7d-a3cc-3a01d65c49a1:5
> Vertices:
> Map 1
> Map Operator Tree:
> TableScan
> alias: test
> Statistics: Num rows: 1 Data size: 13500 Basic stats:
> COMPLETE Column stats: NONE
> GatherStats: false
> Select Operator
> expressions: id (type: int)
> outputColumnNames: id
> Statistics: Num rows: 1 Data size: 13500 Basic stats:
> COMPLETE Column stats: NONE
> Group By Operator
> aggregations: count()
> keys: id (type: int)
> mode: hash
> outputColumnNames: _col0, _col1
> Statistics: Num rows: 1 Data size: 13500 Basic stats:
> COMPLETE Column stats: NONE
> Reduce Output Operator
> key expressions: _col0 (type: int)
> null sort order: a
> sort order: +
> Map-reduce partition columns: _col0 (type: int)
> Statistics: Num rows: 1 Data size: 13500 Basic stats:
> COMPLETE Column stats: NONE
> tag: -1
> TopN: 10
> TopN Hash Memory Usage: 0.1
> value expressions: _col1 (type: bigint)
> auto parallelism: true
> Execution mode: vectorized
> Path -> Alias:
> file:/user/hive/warehouse/test [test]
> Path -> Partition:
> file:/user/hive/warehouse/test
> Partition
> base file name: test
> input format: org.apache.hadoop.mapred.TextInputFormat
> output format:
> org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
> properties:
> COLUMN_STATS_ACCURATE
> {"BASIC_STATS":"true","COLUMN_STATS":{"id":"true"}}
> bucket_count -1
> bucketing_version 2
> column.name.delimiter ,
> columns id
> columns.comments
> columns.types int
> file.inputformat org.apache.hadoop.mapred.TextInputFormat
> file.outputformat
> org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
> location file:/user/hive/warehouse/test
> name default.test
> numFiles 0
> numRows 0
> rawDataSize 0
> serialization.ddl struct test { i32 id}
> serialization.format 1
> serialization.lib
> org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
> totalSize 0
> transient_lastDdlTime 1609730190
> serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
>
> input format: org.apache.hadoop.mapred.TextInputFormat
> output format:
> org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
> properties:
> COLUMN_STATS_ACCURATE
> {"BASIC_STATS":"true","COLUMN_STATS":{"id":"true"}}
> bucket_count -1
> bucketing_version 2
> column.name.delimiter ,
> columns id
> columns.comments
> columns.types int
> file.inputformat
> org.apache.hadoop.mapred.TextInputFormat
> file.outputformat
> org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
> location file:/user/hive/warehouse/test
> name default.test
> numFiles 0
> numRows 0
> rawDataSize 0
> serialization.ddl struct test { i32 id}
> serialization.format 1
> serialization.lib
> org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
> totalSize 0
> transient_lastDdlTime 1609730190
> serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
> name: default.test
> name: default.test
> Truncated Path -> Alias:
> /test [test]
> Reducer 2
> Execution mode: vectorized
> Needs Tagging: false
> Reduce Operator Tree:
> Group By Operator
> aggregations: count(VALUE._col0)
> keys: KEY._col0 (type: int)
> mode: mergepartial
> outputColumnNames: _col0, _col1
> Statistics: Num rows: 1 Data size: 13500 Basic stats:
> COMPLETE Column stats: NONE
> Limit
> Number of rows: 10
> Statistics: Num rows: 1 Data size: 13500 Basic stats:
> COMPLETE Column stats: NONE
> File Output Operator
> compressed: false
> GlobalTableId: 0
> directory:
> file:/tmp/root/7160ea24-52b9-47c3-aafc-c9200263a1c6/hive_2021-01-04_14-15-27_601_190083924675700904-1/-mr-10001/.hive-staging_hive_2021-01-04_14-15-27_601_190083924675700904-1/-ext-10002
> NumFilesPerFileSink: 1
> Statistics: Num rows: 1 Data size: 13500 Basic stats:
> COMPLETE Column stats: NONE
> Stats Publishing Key Prefix:
> file:/tmp/root/7160ea24-52b9-47c3-aafc-c9200263a1c6/hive_2021-01-04_14-15-27_601_190083924675700904-1/-mr-10001/.hive-staging_hive_2021-01-04_14-15-27_601_190083924675700904-1/-ext-10002/
> table:
> input format:
> org.apache.hadoop.mapred.SequenceFileInputFormat
> output format:
> org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
> properties:
> columns _col0,_col1
> columns.types int:bigint
> escape.delim \
> hive.serialization.extend.additional.nesting.levels
> true
> serialization.escape.crlf true
> serialization.format 1
> serialization.lib
> org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
> serde:
> org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
> TotalFiles: 1
> GatherStats: false
> MultiFileSpray: false
> Stage: Stage-0
> Fetch Operator
> limit: 10
> Processor Tree:
> ListSink
> Time taken: 0.102 seconds, Fetched: 143 row(s)
> {code}
>
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