Fuseki Logging

Fuseki logs operation details and also provides a standard NCSA request log.

Logging is via SLF4J over Apache Log4J2, or by the Tomcat configuration if running the WAR file.

NCSA request Log

This log is in NCSA extended/combined log format.
Many web log analysers can process this format.

This log is normally off. The logger name is org.apache.jena.fuseki.Request.

When run as a WAR file inside a webapp container (e.g. Apache Tomcat), the webapp container or reverse proxy will log access requests anyway.

Setting logging

The Fuseki Main engine looks for the log4j2 configuration as follows:

• Use system property log4j2.configurationFile if defined (as usual for log4j2).
• Use file:log4j2.properties (current directory) if it exists
• Use java resource log4j2.properties on the classpath.
• Use java resource org/apache/jena/fuseki/log4j2.properties on the classpath.
• Use a built-in configuration.

The last step is a fallback to catch the case where Fuseki has been repackaged into a new WAR file and org/apache/jena/fuseki/log4j2.properties omitted, or run from the base jar. It is better to include org/apache/jena/fuseki/log4j2.properties.

The preferred customization is to use a custom log4j2.properties file in the directory where Fuseki Main is run.

For the war file packaging, the log4j2.properties should go in FUSEKI_BASE which defaults to /etc/fuseki on Linux.

For the standalone webapp server, FUSEKI_BASE defaults to directory run/ within the directory where the server is run.

The property fuseki.loglogging can also be set to true for additional logging.

Setting ARQ explain logging

Query explanation can be turned on by setting the symbol arq:optReorderBGP in the context to “info”, “fine” or “all”. This can be done in the Assembler file by setting ja:context on the server, dataset, or endpoint:

[] ja:context [ ja:cxtName "arq:logExec" ;  ja:cxtValue "info" ] .

Default setting

The default log4j2.properties.

Logrotate

Below is an example logrotate(1) configuration (to go in /etc/logrotate.d) assuming the log file has been put in /etc/fuseki/logs/fuseki.log.

It rotates the logs once a month, compresses logs on rotation, and keeps them for 6 months.

It uses copytruncate. This may lead to at most one broken log file line.

/etc/fuseki/logs/fuseki.log
{
    compress
    monthly
    rotate 6
    create
    missingok
    copytruncate
    # Date in extension.
    dateext
    # No need
    # delaycompress
}