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From "Boaz Ben-Zvi (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-5728) Hash Aggregate: Useless bigint value vector in the values batch
Date Thu, 17 Aug 2017 23:10:01 GMT
Boaz Ben-Zvi created DRILL-5728:
-----------------------------------

             Summary: Hash Aggregate: Useless bigint value vector in the values batch
                 Key: DRILL-5728
                 URL: https://issues.apache.org/jira/browse/DRILL-5728
             Project: Apache Drill
          Issue Type: Improvement
          Components: Execution - Codegen
    Affects Versions: 1.11.0
            Reporter: Boaz Ben-Zvi
            Priority: Minor


 When aggregating a non-nullable column (like *sum(l_partkey)* below), the code generation
creates an extra value vector (in addition to the actual "sum" vector) which is used as a
"nonNullCount".
   This is useless (as the underlying column is non-nullable), and wastes considerable memory
( 8 * 64K = 512K per each value in a batch !!)

Example query:
<code>
select sum(l_partkey) as slpk from cp.`tpch/lineitem.parquet` group by l_orderkry;
</code>

And as can be seen in the generated code below, the bigint value vector *vv5* is only used
to hold a *1* flag to note "not null":

<code>
        public void updateAggrValuesInternal(int incomingRowIdx, int htRowIdx)
            throws SchemaChangeException
        {
            {
                IntHolder out11 = new IntHolder();
                {
                    out11 .value = vv8 .getAccessor().get((incomingRowIdx));
                }
                IntHolder in = out11;
                work0 .value = vv1 .getAccessor().get((htRowIdx));
                BigIntHolder value = work0;
                work4 .value = vv5 .getAccessor().get((htRowIdx));
                BigIntHolder nonNullCount = work4;
                 
SumFunctions$IntSum_add: {
    nonNullCount.value = 1;
    value.value += in.value;
}
 
                work0 = value;
                vv1 .getMutator().set((htRowIdx), work0 .value);
                work4 = nonNullCount;
                vv5 .getMutator().set((htRowIdx), work4 .value);
            }
        }
</code>

 



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