Monitoring - Practical Cassandra - page 110

Changing Log Levels
If you want to make any changes to the logging schema, you will need to find
the log4jserver.properties file. The default logging level for Cassandra and the
rootLogger is INFO . This level provides a standard amount of information that is
sufficient for understanding the general health of your system. It is definitely help-
ful to see what your system looks like, so you should do so while logging at the
DEBUG level. Be sure not to leave Cassandra in DEBUG mode for production as
the entire system will act noticeably slower. To change the standard logging level
in Cassandra from INFO to DEBUG , change the line that looks like this:
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log4j.rootLogger=INFO,stdout,R
to this:
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log4j.rootLogger=DEBUG,stdout,R
Now your Cassandra node will be running in DEBUG mode. To change it back,
just swap the INFO and DEBUG again. To show less logging, you can change the
logging level to WARN , ERROR , or FATAL .
Example Error
It is worth noting that not all problem messages enter the logs as WARNING or
higher (higher meaning toward FATAL ). Listing 8.1 presents an example of when
things start to go south. This is a common set of log messages that you may see
with your system set at INFO level. Even with the logging level set to INFO , there
is a lot of useful information in the logs. Don't be afraid to keep a regular eye on
the logs so you know what patterns of log messages are normal for your system.
For example, if things are starting to slow down, you may see something like List-
ing 8.1 .
Listing 8.1 INFO Messages That Show Mutation and READ Messages
Dropped
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INFO [ScheduledTasks:1] 2012-07-09
20:48:57,290 MessagingService.java (line 607)