9.23. 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. The distributed plan is shown by default. Each plan fragment of the distributed plan 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 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#
EXPLAIN (TYPE LOGICAL)#
Logical plan:
presto:tiny> EXPLAIN (TYPE LOGICAL) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
-----------------------------------------------------------------------------------------------------------------
Output[regionkey, _col1]
│ Layout: [regionkey:bigint, count:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
│ _col1 := count
└─ RemoteExchange[GATHER]
│ Layout: [regionkey:bigint, count:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
└─ Aggregate(FINAL)[regionkey]
│ Layout: [regionkey:bigint, count:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
│ count := count("count_8")
└─ LocalExchange[HASH][$hashvalue] ("regionkey")
│ Layout: [regionkey:bigint, count_8:bigint, $hashvalue:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
└─ RemoteExchange[REPARTITION][$hashvalue_9]
│ Layout: [regionkey:bigint, count_8:bigint, $hashvalue_9:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
└─ Project[]
│ Layout: [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
│ $hashvalue_10 := "combine_hash"(bigint '0', COALESCE("$operator$hash_code"("regionkey"), 0))
└─ Aggregate(PARTIAL)[regionkey]
│ Layout: [regionkey:bigint, count_8:bigint]
│ count_8 := count(*)
└─ TableScan[tpch:nation:sf0.01]
Layout: [regionkey:bigint]
Estimates: {rows: 25 (225B), cpu: 225, memory: 0B, network: 0B}
regionkey := tpch:regionkey
EXPLAIN (TYPE DISTRIBUTED)#
Distributed plan:
presto:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
------------------------------------------------------------------------------------------------------
Fragment 0 [SINGLE]
Output layout: [regionkey, count]
Output partitioning: SINGLE []
Stage Execution Strategy: UNGROUPED_EXECUTION
Output[regionkey, _col1]
│ Layout: [regionkey:bigint, count:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
│ _col1 := count
└─ RemoteSource[1]
Layout: [regionkey:bigint, count:bigint]
Fragment 1 [HASH]
Output layout: [regionkey, count]
Output partitioning: SINGLE []
Stage Execution Strategy: UNGROUPED_EXECUTION
Aggregate(FINAL)[regionkey]
│ Layout: [regionkey:bigint, count:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
│ count := count("count_8")
└─ LocalExchange[HASH][$hashvalue] ("regionkey")
│ Layout: [regionkey:bigint, count_8:bigint, $hashvalue:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
└─ RemoteSource[2]
Layout: [regionkey:bigint, count_8:bigint, $hashvalue_9:bigint]
Fragment 2 [SOURCE]
Output layout: [regionkey, count_8, $hashvalue_10]
Output partitioning: HASH [regionkey][$hashvalue_10]
Stage Execution Strategy: UNGROUPED_EXECUTION
Project[]
│ Layout: [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
│ Estimates: {rows: ? (?), cpu: ?, memory: ?, network: ?}
│ $hashvalue_10 := "combine_hash"(bigint '0', COALESCE("$operator$hash_code"("regionkey"), 0))
└─ Aggregate(PARTIAL)[regionkey]
│ Layout: [regionkey:bigint, count_8:bigint]
│ count_8 := count(*)
└─ TableScan[tpch:nation:sf0.01, grouped = false]
Layout: [regionkey:bigint]
Estimates: {rows: 25 (225B), cpu: 225, memory: 0B, network: 0B}
regionkey := tpch:regionkey
EXPLAIN (TYPE VALIDATE)#
Validate:
presto:tiny> EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Valid
-------
true
EXPLAIN (TYPE IO)#
IO:
presto:hive> EXPLAIN (TYPE IO, FORMAT JSON) INSERT INTO test_lineitem SELECT * FROM lineitem WHERE shipdate = '2020-02-01' AND quantity > 10;
Query Plan
-----------------------------------
{
inputTableColumnInfos: [
{
table: {
catalog: "hive",
schemaTable: {
schema: "tpch",
table: "test_orders"
}
},
columnConstraints: [
{
columnName: "orderkey",
type: "bigint",
domain: {
nullsAllowed: false,
ranges: [
{
low: {
value: "1",
bound: "EXACTLY"
},
high: {
value: "1",
bound: "EXACTLY"
}
},
{
low: {
value: "2",
bound: "EXACTLY"
},
high: {
value: "2",
bound: "EXACTLY"
}
}
]
}
},
{
columnName: "processing",
type: "boolean",
domain: {
nullsAllowed: false,
ranges: [
{
low: {
value: "false",
bound: "EXACTLY"
},
high: {
value: "false",
bound: "EXACTLY"
}
}
]
}
},
{
columnName: "custkey",
type: "bigint",
domain: {
nullsAllowed: false,
ranges: [
{
low: {
bound: "ABOVE"
},
high: {
value: "10",
bound: "EXACTLY"
}
}
]
}
}
],
estimate: {
outputRowCount: 2,
outputSizeInBytes: 40,
cpuCost: 40,
maxMemory: 0,
networkCost: 0
}
}
],
outputTable: {
catalog: "hive",
schemaTable: {
schema: "tpch",
table: "test_orders"
}
},
estimate: {
outputRowCount: "NaN",
outputSizeInBytes: "NaN",
cpuCost: "NaN",
maxMemory: "NaN",
networkCost: "NaN"
}
}