148 lines
4.8 KiB
Markdown
148 lines
4.8 KiB
Markdown
|
||
# EXPLAIN
|
||
|
||
## 摘要
|
||
|
||
``` sql
|
||
EXPLAIN [ ( option [, ...] ) ] statement
|
||
|
||
where option can be one of:
|
||
|
||
FORMAT { TEXT | GRAPHVIZ | JSON }
|
||
TYPE { LOGICAL | DISTRIBUTED | VALIDATE | IO }
|
||
```
|
||
|
||
## 说明
|
||
|
||
显示语句的逻辑或分布式执行计划，或者对语句进行验证。使用 `TYPE DISTRIBUTED` 选项可以显示分片计划。每个计划片段由单个或多个 openLooKeng 节点执行。片段之间的间隔表示 openLooKeng 节点之间的数据交换。片段类型指定 openLooKeng 节点如何执行片段以及数据如何在片段之间分布：
|
||
|
||
`SINGLE`
|
||
|
||
片段在单个节点上执行。
|
||
|
||
`HASH`
|
||
|
||
片段在固定数量的节点上执行，输入数据通过哈希函数进行分布。
|
||
|
||
`ROUND_ROBIN`
|
||
|
||
片段在固定数量的节点上执行，输入数据以轮循方式进行分布。
|
||
|
||
`BROADCAST`
|
||
|
||
片段在固定数量的节点上执行，输入数据广播到所有节点。
|
||
|
||
`SOURCE`
|
||
|
||
片段在访问输入分段的节点上执行。
|
||
|
||
## 示例
|
||
|
||
逻辑计划：
|
||
|
||
``` sql
|
||
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$hash_code"("regionkey"), 0))
|
||
- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
|
||
count_8 := "count"(*)
|
||
- TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint]
|
||
regionkey := tpch:regionkey
|
||
```
|
||
|
||
分布式计划：
|
||
|
||
``` sql
|
||
lk:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
|
||
Query Plan
|
||
----------------------------------------------------------------------------------------------
|
||
Fragment 0 [SINGLE]
|
||
Output layout: [regionkey, count]
|
||
Output partitioning: SINGLE []
|
||
- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
|
||
_col1 := count
|
||
- RemoteSource[1] => [regionkey:bigint, count:bigint]
|
||
|
||
Fragment 1 [HASH]
|
||
Output layout: [regionkey, count]
|
||
Output partitioning: SINGLE []
|
||
- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
|
||
count := "count"("count_8")
|
||
- LocalExchange[HASH][$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
|
||
```
|
||
|
||
验证：
|
||
|
||
``` sql
|
||
lk:tiny> EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;
|
||
Valid
|
||
-------
|
||
true
|
||
```
|
||
|
||
IO：
|
||
|
||
``` sql
|
||
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"
|
||
}
|
||
}
|
||
}
|
||
```
|
||
|
||
## 另请参见
|
||
|
||
[EXPLAIN ANALYZE](./explain-analyze.md) |