Source: https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/log/
Documentation version: v5.3.2

# Logging statement

The logging statement prints information during [procedure](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/procedures/create/) execution for debugging or monitoring purposes. You can specify the log level, location, and content based on the context of the procedure you create.

The log levels, sorted from lowest to highest severity, are `DEBUG`<`INFO`<`WARN`<`ERROR`<`FATAL`. The corresponding keywords in the log statement are:

- `LOG_DEBUG`: Specify this level to print debug information. Disabled by default. 
- `LOG_INFO`: Specifies this level to print regular operational information that indicates procedures are working as expected. Enabled by default.
- `LOG_WARN`: Specify this level to print warnings about potential problems. Enabled by default.
- `LOG_ERROR`: Specify this level to print errors that disrupt core functionality. Enabled by default.
- `LOG_FATAL`: Specify this level to print fatal errors that halt the procedure. Enabled by default. This level of log will terminate the procedure execution.

By default, `INFO` is set as the minimum log level so that only logs at that level or higher can be printed. To change the minimum level, see [Configure the minimum log level](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/executions/limits/#configure_the_minimum_log_level).

Note

Each procedure is limited to a maximum log size of `64MB`. Minimize logging in [PER NODE](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/match-compute/#then_for_node) or [PER PATH](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/match-compute/#then_for_path) clauses when processing large graphs to avoid exceeding this limit.

## Syntax

diagramsource

 log_statement  

````
log_statement ::= ('LOG_DEBUG' | 'LOG_INFO' | 'LOG_WARN' | 'LOG_ERROR' | 'LOG_FATAL') '(' log_message (',' log_message)* ')' 

````

## Parameters

### `log_message`

The message module in the log. Multiple modules can form a log, separated by commas (`,`). Each module can contain a variable name or literal.

Supported variable types (must be defined before using the log statement):

- [Primitive value variable](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/variable-definition/value-variable/)
- [Aggregate value variable](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/variable-definition/agg/)
- [Node variable](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/patterns/node-patterns/)
- [Edge variable](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/patterns/edge-patterns/)

Supported [literal](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/fe/literals/) types:

- Numeric
- Character string (must be enclosed by double quotes `"`)
- Boolean
- Temporal
- List

## Examples

The following example is based on the temporary graph `#movie_temporary_graph` created in [CREATE TEMPORARY GRAPH](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/ddl/graph-projection/create/).

### Print logs with a variable

````
'''
USE #movie_temporary_graph { 
  VALUE w SumAgg<INT> = 0 
  MATCH ()-[e:Watch]-() 
  PER PATH { 
    SET @w += 1 
  } 
  LOG_INFO("Finish Iteration") 
  LOG_WARN("Final w: ", @w) 
  RETURN @w AS watch_count 
}
'''

````

Return:

````
+-------------+
| watch_count |
+-------------+
| 7820        |
+-------------+
Log:
2025-07-23T07:45:28.432266 INFO  - Finish Iteration
2025-07-23T07:45:28.432531 WARN  - Final w: 7820

````

### Print a `FATAL` log

````
'''
USE #movie_temporary_graph { 
  LOG_DEBUG("This is a debug log") 
  LOG_INFO("This is an info log") 
  LOG_WARN("This is a warning log") 
  LOG_ERROR("This is an error log") 
  LOG_FATAL("This is a fatal log") 
}
'''

````

Return:

````
Error: [NP101]: Procedure error: 2025-07-22T06:38:13.247332 FATAL - This is a fatal log

````

The preceding statement terminates the procedure execution, returns an error, and prints a `FATAL` log.