ARQ - Logging

ARQ uses SLF4j as the logging API and the query and RIOT commands use Log4J2 as a deployment system. You can use Java 1.4 logging instead.

ARQ does not output any logging messages at level INFO in normal operation. The code uses level TRACE and DEBUG. Running with logging set to an application at INFO will cause no output in normal operation. Output below INFO can be very verbose and is intended mainly to help debug ARQ. WARN and FATAL messages are only used when something is wrong.

The root of all the loggers is org.apache.jena. org.apache.jena.query is the application API. org.apache.jena.sparql is the implementation and extensions points.

If using in Tomcat, or other system that provides complex class loading arrangements, be careful about loading from jars in both the web application and the system directories as this can cause separate logging systems to be created (this may not matter).

The ARQ and RIOT command line utilities look for a file “log4j2.properties” in the current directory to control logging during command execution. There is also a built-in configuration so no configuration work is required.

The reading of log4j2.properties from the current directory is achieved by a call to org.apache.jena.atlas.logging.Log.setlog4j2().

Example log4j2.properties file:

status = error
name = PropertiesConfig
filters = threshold

filter.threshold.type = ThresholdFilter
filter.threshold.level = INFO

appender.console.type = Console
appender.console.name = STDOUT
appender.console.layout.type = PatternLayout
appender.console.layout.pattern = %d{HH:mm:ss} %-5p %-15c{1} :: %m%n

rootLogger.level                  = INFO
rootLogger.appenderRef.stdout.ref = STDOUT

logger.jena.name  = org.apache.jena
logger.jena.level = INFO

logger.arq-exec.name  = org.apache.jena.arq.exec
logger.arq-exec.level = INFO

logger.arq-info.name  = org.apache.jena.arq.info
logger.arq-info.level = INFO

logger.riot.name  = org.apache.jena.riot
logger.riot.level = INFO

A Fuseki server output can include ARQ execution logging, see Fuseki logging for the configuration.

Execution Logging

ARQ can log query and update execution details globally or for an individual operations. This adds another level of control on top of the logger level controls.

Explanatory messages are controlled by the Explain.InfoLevel level in the execution context.

The logger used is called org.apache.jena.arq.exec. Message are sent at level “info”. So for log4j2, the following can be set in the log4j2.properties file:

logger.arq-exec.name  = org.apache.jena.arq.exec
logger.arq-exec.level = INFO

The context setting is for key (Java constant) ARQ.symLogExec. To set globally:

ARQ.setExecutionLogging(Explain.InfoLevel.ALL);

and it may also be set on an individual query execution using its local context.

 try(QueryExecution qExec = QueryExecution.create()... .set(ARQ.symLogExec, Explain.InfoLevel.ALL).build) {
    ...
 }

On the command line:

 arq.query --explain --data data file --query=queryfile

The command tdbquery takes the same --explain argument.

Information levels

These can be specified as string, to the command line tools, or using the constants in Explain.InfoLevel.

 qExec.getContext().set(ARQ.symLogExec, Explain.InfoLevel.FINE);

 arq.query --set arq:logExec=FINE --data data file --query=queryfile

ARQ documentation index