159 lines
5.0 KiB
Markdown
159 lines
5.0 KiB
Markdown
+++
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title = "EXPLAIN"
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EXPLAIN
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=======
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Synopsis
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--------
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``` sql
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EXPLAIN [ ( option [, ...] ) ] statement
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where option can be one of:
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FORMAT { TEXT | GRAPHVIZ | JSON }
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TYPE { LOGICAL | DISTRIBUTED | VALIDATE | IO }
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```
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Description
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-----------
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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
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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:
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`SINGLE`
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Fragment is executed on a single node.
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`HASH`
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Fragment is executed on a fixed number of nodes with the input data distributed using a hash function.
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`ROUND_ROBIN`
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Fragment is executed on a fixed number of nodes with the input data distributed in a round-robin fashion.
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`BROADCAST`
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Fragment is executed on a fixed number of nodes with the input data broadcasted to all nodes.
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`SOURCE`
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Fragment is executed on nodes where input splits are accessed.
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Examples
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--------
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Logical plan:
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``` sql
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lk:tiny> EXPLAIN SELECT regionkey, count(*) FROM nation GROUP BY 1;
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Query Plan
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----------------------------------------------------------------------------------------------------------
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- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
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_col1 := count
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- RemoteExchange[GATHER] => regionkey:bigint, count:bigint
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- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
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count := "count"("count_8")
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- LocalExchange[HASH][$hashvalue] ("regionkey") => regionkey:bigint, count_8:bigint, $hashvalue:bigint
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- RemoteExchange[REPARTITION][$hashvalue_9] => regionkey:bigint, count_8:bigint, $hashvalue_9:bigint
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- Project[] => [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
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$hashvalue_10 := "combine_hash"(BIGINT '0', COALESCE("$operator$hash_code"("regionkey"), 0))
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- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
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count_8 := "count"(*)
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- TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint]
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regionkey := tpch:regionkey
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```
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Distributed plan:
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``` sql
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lk:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
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Query Plan
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----------------------------------------------------------------------------------------------
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Fragment 0 [SINGLE]
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Output layout: [regionkey, count]
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Output partitioning: SINGLE []
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- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
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_col1 := count
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- RemoteSource[1] => [regionkey:bigint, count:bigint]
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Fragment 1 [HASH]
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Output layout: [regionkey, count]
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Output partitioning: SINGLE []
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- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
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count := "count"("count_8")
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- LocalExchange[HASH][$hashvalue] ("regionkey") => regionkey:bigint, count_8:bigint, $hashvalue:bigint
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- RemoteSource[2] => [regionkey:bigint, count_8:bigint, $hashvalue_9:bigint]
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Fragment 2 [SOURCE]
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Output layout: [regionkey, count_8, $hashvalue_10]
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Output partitioning: HASH [regionkey][$hashvalue_10]
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- Project[] => [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
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$hashvalue_10 := "combine_hash"(BIGINT '0', COALESCE("$operator$hash_code"("regionkey"), 0))
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- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
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count_8 := "count"(*)
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- TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint]
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regionkey := tpch:regionkey
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```
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Validate:
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``` sql
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lk:tiny> EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;
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Valid
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-------
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true
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```
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IO:
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``` sql
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lk:hive> EXPLAIN (TYPE IO, FORMAT JSON) INSERT INTO test_nation SELECT * FROM nation WHERE regionkey = 2;
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Query Plan
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-----------------------------------
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{
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"inputTableColumnInfos" : [ {
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"table" : {
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"catalog" : "hive",
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"schemaTable" : {
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"schema" : "tpch",
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"table" : "nation"
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}
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},
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"columns" : [ {
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"columnName" : "regionkey",
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"type" : "bigint",
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"domain" : {
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"nullsAllowed" : false,
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"ranges" : [ {
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"low" : {
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"value" : "2",
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"bound" : "EXACTLY"
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},
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"high" : {
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"value" : "2",
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"bound" : "EXACTLY"
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}
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} ]
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}
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} ]
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} ],
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"outputTable" : {
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"catalog" : "hive",
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"schemaTable" : {
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"schema" : "tpch",
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"table" : "test_nation"
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}
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}
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}
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```
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See Also
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--------
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[explain-analyze](./explain-analyze.html)
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