EXPLAIN
Synopsis
EXPLAIN [ ( option [, ...] ) ] statement
where option can be one of:
FORMAT { TEXT | GRAPHVIZ | JSON }
TYPE { LOGICAL | DISTRIBUTED | VALIDATE | IO }
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
openLooKeng nodes. Fragments separation represent the data exchange between openLooKeng nodes. Fragment type specifies how the fragment is executed by openLooKeng nodes and how the data is distributed between fragments:
SINGLE
Fragment is executed on a single node.
HASH
Fragment is executed on a fixed number of nodes with the input data distributed using a hash function.
ROUND_ROBIN
Fragment is executed on a fixed number of nodes with the input data distributed in a round-robin fashion.
BROADCAST
Fragment is executed on a fixed number of nodes with the input data broadcasted to all nodes.
SOURCE
Fragment is executed on nodes where input splits are accessed.
Examples
Logical plan:
lk: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$hash_code"("regionkey"), 0))
- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
count_8 := "count"(*)
- TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint]
regionkey := tpch:regionkey
Distributed plan:
lk:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
----------------------------------------------------------------------------------------------
Fragment 0 [SINGLE]
Output layout: [regionkey, count]
Output partitioning: SINGLE []
- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
_col1 := count
- RemoteSource[1] => [regionkey:bigint, count:bigint]
Fragment 1 [HASH]
Output layout: [regionkey, count]
Output partitioning: SINGLE []
- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
count := "count"("count_8")
- LocalExchange[HASH][$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:
lk:tiny> EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Valid
-------
true
IO:
lk:hive> EXPLAIN (TYPE IO, FORMAT JSON) INSERT INTO test_nation SELECT * FROM nation WHERE regionkey = 2;
Query Plan
-----------------------------------
{
"inputTableColumnInfos" : [ {
"table" : {
"catalog" : "hive",
"schemaTable" : {
"schema" : "tpch",
"table" : "nation"
}
},
"columns" : [ {
"columnName" : "regionkey",
"type" : "bigint",
"domain" : {
"nullsAllowed" : false,
"ranges" : [ {
"low" : {
"value" : "2",
"bound" : "EXACTLY"
},
"high" : {
"value" : "2",
"bound" : "EXACTLY"
}
} ]
}
} ]
} ],
"outputTable" : {
"catalog" : "hive",
"schemaTable" : {
"schema" : "tpch",
"table" : "test_nation"
}
}
}
