EXPLAIN和PROFILEGraph

EXPLAIN语句输出nGQL语句的执行计划，但不会执行nGQL语句。

PROFILE语句执行nGQL语句，然后输出执行计划和执行概要。您可以根据执行计划和执行概要优化查询性能。

执行计划Graph

执行计划由NebulaGraph查询引擎中的执行计划器决定。

执行计划器将解析后的nGQL语句处理为action。action是最小的执行单元。典型的action包括获取指定点的所有邻居、获取边的属性、根据条件过滤点或边等。每个action都被分配给一个operator。

例如SHOW TAGS语句分为两个action，operator为Start和ShowTags。更复杂的GO语句可能会被处理成10个以上的action。

语法Graph

• EXPLAIN

  EXPLAIN [format="row" | "dot"] <your_nGQL_statement>;
  

• PROFILE

  PROFILE [format="row" | "dot"] <your_nGQL_statement>;
  

输出格式Graph

EXPLAIN或PROFILE语句的输出有两种格式：row（默认）和dot。您可以使用format选项修改输出格式。

row格式Graph

row格式将返回信息输出到一个表格中。

• EXPLAIN

  nebula> EXPLAIN format="row" SHOW TAGS;
  Execution succeeded (time spent 327/892 us)
  
  Execution Plan
  
  -----+----------+--------------+----------------+----------------------------------------------------------------------
  | id | name     | dependencies | profiling data | operator info                                                       |
  -----+----------+--------------+----------------+----------------------------------------------------------------------
  |  1 | ShowTags | 0            |                | outputVar: [{"colNames":[],"name":"__ShowTags_1","type":"DATASET"}] |
  |    |          |              |                | inputVar:                                                           |
  -----+----------+--------------+----------------+----------------------------------------------------------------------
  |  0 | Start    |              |                | outputVar: [{"colNames":[],"name":"__Start_0","type":"DATASET"}]    |
  -----+----------+--------------+----------------+----------------------------------------------------------------------
  

• PROFILE

  nebula> PROFILE format="row" SHOW TAGS;
  +--------+
  | Name   |
  +--------+
  | player |
  +--------+
  | team   |
  +--------+
  Got 2 rows (time spent 2038/2728 us)
  
  Execution Plan
  
  -----+----------+--------------+----------------------------------------------------+----------------------------------------------------------------------
  | id | name     | dependencies | profiling data                                     | operator info                                                       |
  -----+----------+--------------+----------------------------------------------------+----------------------------------------------------------------------
  |  1 | ShowTags | 0            | ver: 0, rows: 1, execTime: 42us, totalTime: 1177us | outputVar: [{"colNames":[],"name":"__ShowTags_1","type":"DATASET"}] |
  |    |          |              |                                                    | inputVar:                                                           |
  -----+----------+--------------+----------------------------------------------------+----------------------------------------------------------------------
  |  0 | Start    |              | ver: 0, rows: 0, execTime: 1us, totalTime: 57us    | outputVar: [{"colNames":[],"name":"__Start_0","type":"DATASET"}]    |
  -----+----------+--------------+----------------------------------------------------+----------------------------------------------------------------------
  

dot格式Graph

dot格式将返回DOT语言的信息，然后您可以使用Graphviz生成计划图。

说明：Graphviz是一款开源可视化图工具，可以绘制DOT语言脚本描述的图。Graphviz提供一个在线工具，可以预览DOT语言文件，并将它们导出为SVG或JSON等其他格式。详情请参见Graph。

nebula> EXPLAIN format="dot" SHOW TAGS;
Execution succeeded (time spent 161/665 us)
Execution Plan
---------------------------------------------------------------------------------------------------------------------------------------------  -------------
  plan
---------------------------------------------------------------------------------------------------------------------------------------------  -------------
  digraph exec_plan {
      rankdir=LR;
      "ShowTags_0"[label="ShowTags_0|outputVar: \[\{\"colNames\":\[\],\"name\":\"__ShowTags_0\",\"type\":\"DATASET\"\}\]\l|inputVar:\l",   shape=Mrecord];
      "Start_2"->"ShowTags_0";
      "Start_2"[label="Start_2|outputVar: \[\{\"colNames\":\[\],\"name\":\"__Start_2\",\"type\":\"DATASET\"\}\]\l|inputVar: \l",   shape=Mrecord];
  }
---------------------------------------------------------------------------------------------------------------------------------------------  -------------

将上述示例的DOT语言转换为Graphviz图，如下所示。