EXPLAIN and PROFILE¶

EXPLAIN helps output the execution plan of an nGQL statement without executing the statement.

PROFILE executes the statement, then outputs the execution plan as well as the execution profile. You can optimize the queries for better performance according to the execution plan and profile.

Execution Plan¶

The execution plan is determined by the execution planner in the Nebula Graph query engine.

The execution planner processes the parsed nGQL statements into actions. An action is the smallest unit that can be executed. A typical action fetches all neighbors of a given vertex, gets the properties of an edge, and filters vertices or edges based on the given conditions. Each action is assigned to an operator that performs the action.

For example, a SHOW TAGS statement is processed into two actions and assigned to a Start operator and a ShowTags operator, while a more complex GO statement may be processed into more than 10 actions and assigned to 10 operators.

Syntax¶

• EXPLAIN

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

• PROFILE

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

Output formats¶

The output of an EXPLAIN or a PROFILE statement has two formats, the default row format and the dot format. You can use the format option to modify the output format. Omitting the format option indicates using the default row format.

The row format¶

The row format outputs the return message in a table as follows.

• 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"}]    |
  -----+----------+--------------+----------------------------------------------------+----------------------------------------------------------------------
  

The descriptions are as follows.

The dot format¶

You can use the format="dot" option to output the return message in the dot language, and then use Graphviz to generate a graph of the plan.

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];
  }
---------------------------------------------------------------------------------------------------------------------------------------------  -------------

The Graphviz graph transformed from the above DOT statement is as follows.