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 Trino nodes. Fragments separation represent the data exchange between Trino nodes. Fragment type specifies how the fragment is executed by Trino 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:

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:

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:

EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;

 Valid
-------
 true

EXPLAIN (TYPE IO)#

IO:

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"
   }
}