EXPLAIN

摘要

  1. EXPLAIN [ ( option [, ...] ) ] statement
  3. where option can be one of:
  5.     FORMAT { TEXT | GRAPHVIZ | JSON }
  6.     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：

  1. lk:tiny> EXPLAIN SELECT regionkey, count(*) FROM nation GROUP BY 1;
  2.                                                 Query Plan
  3. ----------------------------------------------------------------------------------------------------------
  4.  - Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
  5.          _col1 := count
  6.      - RemoteExchange[GATHER] => regionkey:bigint, count:bigint
  7.          - Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
  8.                 count := "count"("count_8")
  9.              - LocalExchange[HASH][$hashvalue] ("regionkey") => regionkey:bigint, count_8:bigint, $hashvalue:bigint
  10.                  - RemoteExchange[REPARTITION][$hashvalue_9] => regionkey:bigint, count_8:bigint, $hashvalue_9:bigint
  11.                      - Project[] => [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
  12.                              $hashvalue_10 := "combine_hash"(BIGINT '0', COALESCE("$operator$hash_code"("regionkey"), 0))
  13.                          - Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
  14.                                  count_8 := "count"(*)
  15.                              - TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint]
  16.                                      regionkey := tpch:regionkey

分布式计划：

  1. lk:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
  2.                                           Query Plan
  3. ----------------------------------------------------------------------------------------------
  4.  Fragment 0 [SINGLE]
  5.      Output layout: [regionkey, count]
  6.      Output partitioning: SINGLE []
  7.      - Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
  8.              _col1 := count
  9.          - RemoteSource[1] => [regionkey:bigint, count:bigint]
  11.  Fragment 1 [HASH]
  12.      Output layout: [regionkey, count]
  13.      Output partitioning: SINGLE []
  14.      - Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
  15.              count := "count"("count_8")
  16.          - LocalExchange[HASH][$hashvalue] ("regionkey") => regionkey:bigint, count_8:bigint, $hashvalue:bigint
  17.              - RemoteSource[2] => [regionkey:bigint, count_8:bigint, $hashvalue_9:bigint]
  19.  Fragment 2 [SOURCE]
  20.      Output layout: [regionkey, count_8, $hashvalue_10]
  21.      Output partitioning: HASH [regionkey][$hashvalue_10]
  22.      - Project[] => [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
  23.              $hashvalue_10 := "combine_hash"(BIGINT '0', COALESCE("$operator$hash_code"("regionkey"), 0))
  24.          - Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
  25.                  count_8 := "count"(*)
  26.              - TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] => [regionkey:bigint]
  27.                      regionkey := tpch:regionkey

验证：

  1. lk:tiny> EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;
  2.  Valid
  3. -------
  4.  true

IO：

  1. lk:hive> EXPLAIN (TYPE IO, FORMAT JSON) INSERT INTO test_nation SELECT * FROM nation WHERE regionkey = 2;
  2.             Query Plan
  3. -----------------------------------
  4.  {
  5.    "inputTableColumnInfos" : [ {
  6.      "table" : {
  7.        "catalog" : "hive",
  8.        "schemaTable" : {
  9.          "schema" : "tpch",
  10.          "table" : "nation"
  11.        }
  12.      },
  13.      "columns" : [ {
  14.        "columnName" : "regionkey",
  15.        "type" : "bigint",
  16.        "domain" : {
  17.          "nullsAllowed" : false,
  18.          "ranges" : [ {
  19.            "low" : {
  20.              "value" : "2",
  21.              "bound" : "EXACTLY"
  22.            },
  23.            "high" : {
  24.              "value" : "2",
  25.              "bound" : "EXACTLY"
  26.            }
  27.          } ]
  28.        }
  29.      } ]
  30.    } ],
  31.    "outputTable" : {
  32.      "catalog" : "hive",
  33.      "schemaTable" : {
  34.        "schema" : "tpch",
  35.        "table" : "test_nation"
  36.      }
  37.    }
  38.  }

另请参见

EXPLAIN ANALYZE