https://community.cloudera.com/t5/Support-Questions/What-is-col0-in-hive-explain-plan/m-p/191214#M153303 <P>Hello,</P><P>I am trying to better understand hive explain and hive performance. I have a simple count(*) that is failing with OOM. Rather than just increasing tez container size memory, im trying to understand why its failing. Explain plan below:</P><P>It looks like its grouping by _col0. What is the real name of this column? Is there a way to find out?</P><PRE>+----------------------------------------------------+ | Explain | +----------------------------------------------------+ | Plan optimized by CBO. | | | | Vertex dependency in root stage | | Reducer 2 &lt;- Map 1 (CUSTOM_SIMPLE_EDGE) | | | | Stage-0 | | Fetch Operator | | limit:-1 | | Stage-1 | | Reducer 2 | | File Output Operator [FS_6] | | Group By Operator [GBY_4] (rows=1 width=8) | | Output:["_col0"],aggregations:["count(VALUE._col0)"] | | &lt;-Map 1 [CUSTOM_SIMPLE_EDGE] | | PARTITION_ONLY_SHUFFLE [RS_3] | | Group By Operator [GBY_2] (rows=1 width=8) | | Output:["_col0"],aggregations:["count()"] | | Select Operator [SEL_1] (rows=1 width=53922865152) | | TableScan [TS_0] (rows=1 width=53922865152) | | db1@tb1,tb1,Tbl:COMPLETE,Col:COMPLETE | </PRE> Tue, 15 May 2018 04:22:29 GMT crayonml 2018-05-15T04:22:29Z