======= EXPLAIN ======= Synopsis -------- .. code-block:: none EXPLAIN [ ( option [, ...] ) ] statement where option can be one of: FORMAT { TEXT | GRAPHVIZ } TYPE { LOGICAL | DISTRIBUTED | VALIDATE } Description ----------- Show the logical or distributed execution plan of a statement, or validate the statement. Use ``TYPE DISTRIBUTED`` option to display fragmented plan. Each plan fragment is executed by a single or multiple Presto nodes. Fragments separation represent the data exchange between Presto nodes. Fragment type specifies how the fragment is executed by Presto nodes and how the data is distributed between fragments: * ``SINGLE``: Fragment is executed by single node. * ``HASH``: Fragment is executed by a fixed number of Presto nodes. Fragment input data is distributed among nodes with a hash function. * ``ROUND_ROBIN``: Fragment is executed by a fixed number of Presto nodes. Fragment input data is distributed among nodes with a round robin function. * ``BROADCAST``: Fragment is executed by a fixed number of Presto nodes. Fragment input data is broadcasted to all nodes. * ``SOURCE``: Fragment is executed on nodes where input splits needs to be accessed from. Examples -------- Logical plan: .. code-block:: none presto:tiny> EXPLAIN SELECT regionkey, count(*) FROM nation GROUP BY 1; Query Plan ---------------------------------------------------------------------------------------------------------- - Output[regionkey, _col1] => [regionkey:bigint, count:bigint] _col1 := count - RemoteExchange[GATHER] => regionkey:bigint, count:bigint - Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint] count := "count"("count_8") - LocalExchange[HASH][$hashvalue] ("regionkey") => regionkey:bigint, count_8:bigint, $hashvalue:bigint - RemoteExchange[REPARTITION][$hashvalue_9] => regionkey:bigint, count_8:bigint, $hashvalue_9:bigint - Project[] => [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint] $hashvalue_10 := "combine_hash"(BIGINT '0', COALESCE("$operator$hash_code"("regionkey"), 0)) - Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint] count_8 := "count"(*) - TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint] regionkey := tpch:regionkey Distributed plan: .. code-block:: none presto:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1; Query Plan ---------------------------------------------------------------------------------------------- Fragment 0 [SINGLE] Output layout: [regionkey, count] Output partitioning: SINGLE [] - Output[regionkey, _col1] => [regionkey:bigint, count:bigint] _col1 := count - RemoteSource[1] => [regionkey:bigint, count:bigint] Fragment 1 [HASH] Output layout: [regionkey, count] Output partitioning: SINGLE [] - Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint] count := "count"("count_8") - LocalExchange[HASH][$hashvalue] ("regionkey") => regionkey:bigint, count_8:bigint, $hashvalue:bigint - RemoteSource[2] => [regionkey:bigint, count_8:bigint, $hashvalue_9:bigint] Fragment 2 [SOURCE] Output layout: [regionkey, count_8, $hashvalue_10] Output partitioning: HASH [regionkey][$hashvalue_10] - Project[] => [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint] $hashvalue_10 := "combine_hash"(BIGINT '0', COALESCE("$operator$hash_code"("regionkey"), 0)) - Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint] count_8 := "count"(*) - TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint] regionkey := tpch:regionkey Validate: .. code-block:: none presto:tiny> EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1; Valid ------- true See Also -------- :doc:`explain-analyze`