EXPLAIN¶
概要¶
EXPLAIN [ ( option [, ...] ) ] statement
其中 option 可以是下列其中一個
FORMAT { TEXT | GRAPHVIZ | JSON }
TYPE { LOGICAL | DISTRIBUTED | VALIDATE | IO }
描述¶
顯示陳述式的邏輯或分散式執行計畫，或驗證陳述式。使用 TYPE DISTRIBUTED 選項顯示分散式計畫。每個計畫片段都由單個或多個 Presto 節點執行。片段分隔表示 Presto 節點之間的資料交換。片段類型指定 Presto 節點如何執行片段，以及如何在片段之間分配資料
SINGLE片段在單個節點上執行。
HASH片段在固定數量的節點上執行，並使用雜湊函式分配輸入資料。
ROUND_ROBIN片段在固定數量的節點上執行，並以循環配置方式分配輸入資料。
BROADCAST片段在固定數量的節點上執行，輸入資料會廣播到所有節點。
SOURCE片段在存取輸入分割的節點上執行。
範例¶
邏輯計畫
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$hash_code"("regionkey"), 0))
- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
count_8 := "count"(*)
- TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint]
regionkey := tpch:regionkey
分散式計畫
presto:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
----------------------------------------------------------------------------------------------
Fragment 0 [SINGLE]
Output layout: [regionkey, count]
Output partitioning: SINGLE []
- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
_col1 := count
- RemoteSource[1] => [regionkey:bigint, count:bigint]
Fragment 1 [HASH]
Output layout: [regionkey, count]
Output partitioning: SINGLE []
- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
count := "count"("count_8")
- LocalExchange[HASH][$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
驗證
presto:tiny> EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;
result
-------
true
IO
presto: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"
}
}
}