Support reduction_fator metric (for EXPLAIN ANALYZE) in AggregateExec #18410
Description
Is your feature request related to a problem or challenge?
In the pre-aggregation stage (In datafusion's implementation, AggregateExec with Partial mode), a reduction_factor can be calculated as output_rows (after partial aggregation) / input_rows in AggregateExec
Background for 'partial aggregation':
Example with datafusion-cli
> set datafusion.explain.analyze_level = summary;
0 row(s) fetched.
Elapsed 0.000 seconds.
> create table t1(a int, b int);
0 row(s) fetched.
Elapsed 0.007 seconds.
> insert into t1 values (1,10), (1, 20), (2,10), (2,30);
+-------+
| count |
+-------+
| 4 |
+-------+
1 row(s) fetched.
Elapsed 0.011 seconds.
> explain analyze select a, sum(b)
from t1
group by a;
+-------------------+---------------------------------------------------------------------------------------------------------------------------------------------------+
| plan_type | plan |
+-------------------+---------------------------------------------------------------------------------------------------------------------------------------------------+
| Plan with Metrics | AggregateExec: mode=FinalPartitioned, gby=[a@0 as a], aggr=[sum(t1.b)], metrics=[output_rows=2, elapsed_compute=4.67121ms, output_bytes=1088.0 B] |
| | CoalesceBatchesExec: target_batch_size=8192, metrics=[output_rows=2, elapsed_compute=17.875µs, output_bytes=192.0 KB] |
| | RepartitionExec: partitioning=Hash([a@0], 14), input_partitions=14, metrics=[] |
| | RepartitionExec: partitioning=RoundRobinBatch(14), input_partitions=1, metrics=[] |
| | AggregateExec: mode=Partial, gby=[a@0 as a], aggr=[sum(t1.b)], metrics=[output_rows=2, elapsed_compute=1.931542ms, output_bytes=544.0 B] |
| | DataSourceExec: partitions=1, partition_sizes=[1], metrics=[] |
| | |
+-------------------+---------------------------------------------------------------------------------------------------------------------------------------------------+
1 row(s) fetched.
Elapsed 0.018 seconds.
You can see for the bottom AggregateExec with Partial mode, it has 4 input rows, and after the pre-aggregation, the output size has been reduced to 2 rows, so a reduction_factor metric can be calculated as 4/2 => 2, indicating on average each group has 2 origianl rows.
Describe the solution you'd like
Add reduction_factor metric for AggregateExec with Partial mode.
Reference PR: #18406
Describe alternatives you've considered
No response
Additional context
No response