5.4. Logging Attributes

5.4.1. About Log Levels

Log levels are an ordered set of enumerated values that indicate the nature and severity of a log message. The level of a given log message is specified by the developer using the appropriate methods of their chosen logging framework to send the message.
Red Hat JBoss Data Grid supports all the log levels used by the supported application logging frameworks. The six most commonly used log levels are (ordered by lowest to highest severity):
  1. TRACE
  2. DEBUG
  3. INFO
  4. WARN
  5. ERROR
  6. FATAL
Log levels are used by log categories and handlers to limit the messages they are responsible for. Each log level has an assigned numeric value which indicates its order relative to other log levels. Log categories and handlers are assigned a log level and they only process log messages of that numeric value or higher. For example a log handler with the level of WARN will only record messages of the levels WARN, ERROR and FATAL.

5.4.2. Supported Log Levels

The following table lists log levels that are supported in Red Hat JBoss Data Grid. Each entry includes the log level, its value and description. The log level values indicate each log level's relative value to other log levels. Additionally, log levels in different frameworks may be named differently, but have a log value consistent to the provided list.

Table 5.2. Supported Log Levels

Log Level Value Description
FINEST 300 -
FINER 400 -
TRACE 400 Used for messages that provide detailed information about the running state of an application. TRACE level log messages are captured when the server runs with the TRACE level enabled.
DEBUG 500 Used for messages that indicate the progress of individual requests or activities of an application. DEBUG level log messages are captured when the server runs with the DEBUG level enabled.
FINE 500 -
CONFIG 700 -
INFO 800 Used for messages that indicate the overall progress of the application. Used for application start up, shut down and other major lifecycle events.
WARN 900 Used to indicate a situation that is not in error but is not considered ideal. Indicates circumstances that can lead to errors in the future.
WARNING 900 -
ERROR 1000 Used to indicate an error that has occurred that could prevent the current activity or request from completing but will not prevent the application from running.
SEVERE 1000 -
FATAL 1100 Used to indicate events that could cause critical service failure and application shutdown and possibly cause JBoss Data Grid to shut down.

5.4.3. About Log Categories

Log categories define a set of log messages to capture and one or more log handlers which will process the messages.
The log messages to capture are defined by their Java package of origin and log level. Messages from classes in that package and of that log level or higher (with greater or equal numeric value) are captured by the log category and sent to the specified log handlers. As an example, the WARNING log level results in log values of 900, 1000 and 1100 are captured.
Log categories can optionally use the log handlers of the root logger instead of their own handlers.
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5.4.4. About the Root Logger

The root logger captures all log messages sent to the server (of a specified level) that are not captured by a log category. These messages are then sent to one or more log handlers.
By default the root logger is configured to use a console and a periodic log handler. The periodic log handler is configured to write to the file server.log. This file is sometimes referred to as the server log.

5.4.5. About Log Handlers

Log handlers define how captured log messages are recorded by Red Hat JBoss Data Grid. The six types of log handlers configurable in JBoss Data Grid are:
  • Console
  • File
  • Periodic
  • Size
  • Async
  • Custom
Log handlers direct specified log objects to a variety of outputs (including the console or specified log files). Some log handlers used in JBoss Data Grid are wrapper log handlers, used to direct other log handlers' behavior.
Log handlers are used to direct log outputs to specific files for easier sorting or to write logs for specific intervals of time. They are primarily useful to specify the kind of logs required and where they are stored or displayed or the logging behavior in JBoss Data Grid.

5.4.6. Log Handler Types

The following table lists the different types of log handlers available in Red Hat JBoss Data Grid:

Table 5.3. Log Handler Types

Log Handler Type Description Use Case
Console Console log handlers write log messages to either the host operating system’s standard out (stdout) or standard error (stderr) stream. These messages are displayed when JBoss Data Grid is run from a command line prompt. The Console log handler is preferred when JBoss Data Grid is administered using the command line. In such a case, the messages from a Console log handler are not saved unless the operating system is configured to capture the standard out or standard error stream.
File File log handlers are the simplest log handlers. Their primary use is to write log messages to a specified file. File log handlers are most useful if the requirement is to store all log entries according to the time in one place.
Periodic Periodic file handlers write log messages to a named file until a specified period of time has elapsed. Once the time period has elapsed, the specified time stamp is appended to the file name. The handler then continues to write into the newly created log file with the original name. The Periodic file handler can be used to accumulate log messages on a weekly, daily, hourly or other basis depending on the requirements of the environment.
Size Size log handlers write log messages to a named file until the file reaches a specified size. When the file reaches a specified size, it is renamed with a numeric prefix and the handler continues to write into a newly created log file with the original name. Each size log handler must specify the maximum number of files to be kept in this fashion. The Size handler is best suited to an environment where the log file size must be consistent.
Async Async log handlers are wrapper log handlers that provide asynchronous behavior for one or more other log handlers. These are useful for log handlers that have high latency or other performance problems such as writing a log file to a network file system. The Async log handlers are best suited to an environment where high latency is a problem or when writing to a network file system.
Custom Custom log handlers enable to you to configure new types of log handlers that have been implemented. A custom handler must be implemented as a Java class that extends java.util.logging.Handler and be contained in a module. Custom log handlers create customized log handler types and are recommended for advanced users.
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5.4.7. Selecting Log Handlers

The following are the most common uses for each of the log handler types available for Red Hat JBoss Data Grid:
  • The Console log handler is preferred when JBoss Data Grid is administered using the command line. In such a case, errors and log messages appear on the console window and are not saved unless separately configured to do so.
  • The File log handler is used to direct log entries into a specified file. This simplicity is useful if the requirement is to store all log entries according to the time in one place.
  • The Periodic log handler is similar to the File handler but creates files according to the specified period. As an example, this handler can be used to accumulate log messages on a weekly, daily, hourly or other basis depending on the requirements of the environment.
  • The Size log handler also writes log messages to a specified file, but only while the log file size is within a specified limit. Once the file size reaches the specified limit, log files are written to a new log file. This handler is best suited to an environment where the log file size must be consistent.
  • The Async log handler is a wrapper that forces other log handlers to operate asynchronously. This is best suited to an environment where high latency is a problem or when writing to a network file system.
  • The Custom log handler creates new, customized types of log handlers. This is an advanced log handler.

5.4.8. About Log Formatters

A log formatter is the configuration property of a log handler. The log formatter defines the appearance of log messages that originate from the relevant log handler. The log formatter is a string that uses the same syntax as the java.util.Formatter class.