Did u run "analyze table emp compute statistics" before you run the explain? thanks.
Pengcheng On Wed, Feb 8, 2017 at 9:29 PM, Vivek Sharma <vlsha...@hotmail.com> wrote: > Hi, > > > I am new to Hive (just few days of learning). > > > I am an Oracle Performance Expert and am comparing the Explain feature of > Hive with Oracle Explain Plan command. I have an Internal Table with around > 100 Rows in it. However, the Explain command in Hive computes this as 33, > which looks to be huge discrepancy and cause a performance issues (for a > larger table). Wanted to know the internal calculations of Hive to come out > with the NUM ROWS. The output is pasted below (The table actually has 100 > Rows) : > > > hive (vivek)> explain select country, empno from emp; > OK > Explain > STAGE DEPENDENCIES: > Stage-0 is a root stage > > STAGE PLANS: > Stage: Stage-0 > Fetch Operator > limit: -1 > Processor Tree: > TableScan > alias: emp > Statistics: Num rows: 33 Data size: 3501 Basic stats: COMPLETE > Column stats: NONE > Select Operator > expressions: country (type: string), empno (type: int) > outputColumnNames: _col0, _col1 > Statistics: Num rows: 33 Data size: 3501 Basic stats: COMPLETE > Column stats: NONE > ListSink > > Regards > Vivek > >
