Jinfeng Ni created DRILL-1212:
---------------------------------
Summary: Remove extra exchange operator when generate a two phase
aggregation plan.
Key: DRILL-1212
URL: https://issues.apache.org/jira/browse/DRILL-1212
Project: Apache Drill
Issue Type: Bug
Reporter: Jinfeng Ni
We may see an extra hash exchange operator, when optimizer choose a two phase
aggregation plan, for a query with group by GB_Key order by OB_Key and GB_key
is same as Ob_key.
One example of such plan with extra exchange is TPCH Q12:
select
l.l_shipmode,
sum(case
when o.o_orderpriority = '1-URGENT'
or o.o_orderpriority = '2-HIGH'
then 1
else 0
end) as high_line_count,
sum(case
when o.o_orderpriority <> '1-URGENT'
and o.o_orderpriority <> '2-HIGH'
then 1
else 0
end) as low_line_count
from
cp.`tpch/orders.parquet` o,
cp.`tpch/lineitem.parquet` l
where
o.o_orderkey = l.l_orderkey
and l.l_shipmode in ('TRUCK', 'REG AIR')
and l.l_commitdate < l.l_receiptdate
and l.l_shipdate < l.l_commitdate
and l.l_receiptdate >= date '1994-01-01'
and l.l_receiptdate < date '1994-01-01' + interval '1' year
group by
l.l_shipmode
order by
l.l_shipmode;
The issue is caused by the rule does not propagate the hash distribution up,
and hence introduce unnecessary hash exchange.
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