8.8. EXPLAIN
Synopsis
EXPLAIN [ ( option [, ...] ) ] statement
where option can be one of:
FORMAT { TEXT | GRAPHVIZ }
TYPE { LOGICAL | DISTRIBUTED }
Description
Show the logical or distributed execution plan of a statement.
Examples
Logical plan:
presto:tiny> EXPLAIN SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
----------------------------------------------------------------------------------------------------------
- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
_col1 := count
- Exchange[GATHER] => regionkey:bigint, count:bigint
- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
count := "count"("count_8")
- Exchange[REPARTITION] => regionkey:bigint, count_8:bigint
- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
count_8 := "count"(*)
- TableScan[tpch:tpch:nation:sf0.01, original constraint=true] => [regionkey:bigint]
regionkey := tpch:tpch:regionkey:2
Distributed plan:
presto:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
----------------------------------------------------------------------------------------------
Fragment 2 [SINGLE]
Output layout: [regionkey, count]
- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
_col1 := count
- RemoteSource[1] => [regionkey:bigint, count:bigint]
Fragment 1 [FIXED]
Output layout: [regionkey, count]
- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
count := "count"("count_8")
- RemoteSource[0] => [regionkey:bigint, count_8:bigint]
Fragment 0 [SOURCE]
Output layout: [regionkey, count_8]
Output partitioning: [regionkey]
- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
count_8 := "count"(*)
- TableScan[tpch:tpch:nation:sf0.01, original constraint=true] => [regionkey:bigint]
regionkey := tpch:tpch:regionkey:2