IMPALA-5036: Parquet count star optimization

Instead of materializing empty rows when computing count star, we use
the data stored in the Parquet RowGroup.num_rows field. The Parquet
scanner tuple is modified to have one slot into which we will write the
num rows statistic. The aggregate function is changed from count to a
special sum function that gets initialized to 0. We also add a rewrite
rule so that count(<literal>) is rewritten to count(*) in order to make
sure that this optimization is applied in all cases.

Testing:
- Added functional and planner tests

Change-Id: I536b85c014821296aed68a0c68faadae96005e62
Reviewed-on: http://gerrit.cloudera.org:8080/6812
Reviewed-by: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Tested-by: Impala Public Jenkins

testdata/workloads/functional-query/queries/QueryTest/aggregation.test

@@ -1255,3 +1255,67 @@ where t2.int_col IN (t1.int_col_1, t1.int_col)
 ---- TYPES
 TIMESTAMP,BIGINT
 ====
+---- QUERY
+# IMPALA-5036: Tests the correctness of the Parquet count(*) optimization.
+select count(1)
+from functional_parquet.alltypes
+---- RESULTS
+7300
+---- TYPES
+bigint
+=====
+---- QUERY
+# IMPALA-5036: Parquet count(*) optimization with predicates on the partition columns.
+select count(1)
+from functional_parquet.alltypes where year < 2010 and month > 8
+---- RESULTS
+1220
+---- TYPES
+bigint
+=====
+---- QUERY
+# IMPALA-5036: Parquet count(*) optimization with group by partition columns.
+select year, month, count(1)
+from functional_parquet.alltypes where month > 10 group by year, month
+---- RESULTS
+2009,11,300
+2009,12,310
+2010,11,300
+2010,12,310
+---- TYPES
+int, int, bigint
+=====
+---- QUERY
+# IMPALA-5036: Parquet count(*) optimization with both group by and predicates on
+# partition columns.
+select count(1)
+from functional_parquet.alltypes where year < 2010 and month > 8
+group by month
+---- RESULTS
+310
+300
+310
+300
+---- TYPES
+bigint
+=====
+---- QUERY
+# IMPALA-5036: Parquet count(*) optimization with the result of the going into a join.
+select x.bigint_col from functional.alltypes x
+  inner join (
+    select count(1) as a from functional_parquet.alltypes group by year
+  ) t on x.id = t.a;
+---- RESULTS
+0
+0
+---- TYPES
+bigint
+=====
+---- QUERY
+# IMPALA-5036: Parquet count(*) optimization with the agg function in the having clause.
+select 1 from functional_parquet.alltypes having count(*) > 1
+---- RESULTS
+1
+---- TYPES
+tinyint
+====

testdata/workloads/functional-query/queries/QueryTest/parquet-stats-agg.test

@@ -0,0 +1,117 @@
+====
+---- QUERY
+# Tests the correctness of the Parquet count(*) optimization.
+select count(1)
+from functional_parquet.alltypes
+---- RESULTS
+7300
+---- TYPES
+bigint
+=====
+---- QUERY
+# Parquet count(*) optimization with predicates on the partition columns.
+select count(1)
+from functional_parquet.alltypes where year < 2010 and month > 8
+---- RESULTS
+1220
+---- TYPES
+bigint
+=====
+---- QUERY
+# Parquet count(*) optimization with group by partition columns.
+select year, month, count(1)
+from functional_parquet.alltypes group by year, month
+---- RESULTS
+2009,1,310
+2009,2,280
+2009,3,310
+2009,4,300
+2009,5,310
+2009,6,300
+2009,7,310
+2009,8,310
+2009,9,300
+2009,10,310
+2009,11,300
+2009,12,310
+2010,1,310
+2010,2,280
+2010,3,310
+2010,4,300
+2010,5,310
+2010,6,300
+2010,7,310
+2010,8,310
+2010,9,300
+2010,10,310
+2010,11,300
+2010,12,310
+---- TYPES
+int, int, bigint
+=====
+---- QUERY
+# Parquet count(*) optimization with both group by and predicates on partition columns.
+select count(1)
+from functional_parquet.alltypes where year < 2010 and month > 8
+group by month
+---- RESULTS
+310
+300
+310
+300
+---- TYPES
+bigint
+=====
+---- QUERY
+# Parquet count(*) optimization with the result going into a join.
+select x.bigint_col from functional.alltypes x
+  inner join (
+    select count(1) as a from functional_parquet.alltypes group by year
+  ) t on x.id = t.a;
+---- RESULTS
+0
+0
+---- TYPES
+bigint
+=====
+---- QUERY
+# Parquet count(*) optimization with the agg function in the having clause.
+select 1 from functional_parquet.alltypes having count(*) > 1
+---- RESULTS
+1
+---- TYPES
+tinyint
+====
+---- QUERY
+# Verify that 0 is returned for count(*) on an empty table.
+select count(1) from functional_parquet.emptytable
+---- RESULTS
+0
+---- TYPES
+bigint
+=====
+---- QUERY
+# Verify that 0 is returned when all partitions are pruned.
+select count(1) from functional_parquet.alltypes where year = -1
+---- RESULTS
+0
+---- TYPES
+bigint
+=====
+---- QUERY
+# Test different row group size combinations.
+select count(*) from functional_parquet.lineitem_multiblock
+union all
+select count(*) from functional_parquet.lineitem_multiblock_one_row_group
+union all
+select count(*) from functional_parquet.lineitem_sixblocks
+union all
+select count(*) from tpch_parquet.lineitem
+---- RESULTS
+20000
+40000
+40000
+6001215
+---- TYPES
+bigint
+=====