Skip to main content

Deciding what to log

In this section we will discuss what to log and the various levels at which we can generate log statements.




Even though I have mentioned that we should generate log statements when control enters and exits a method, this is a rather controversial point. Especially generating log statements on exiting; because a method could have multiple exit routes. What do you think? I would say, if in doubt - do NOT generate logs when exiting a method. Logs that show control has entered a method do have value in my personal opinion, however you can leave those out as well if you do not see much value in them.

Let me first draw your attention to the output from last page.

0 [main] DEBUG LoggerTest - Entering main
453 [main] DEBUG LoggerTest - Exiting main

What is DEBUG? As I have explained, we should log several events from our program as it executes. But all events are not equally important. Hence, Log4J supports six levels for logging, where each level is appropriate for a certain type of log statement. The levels are (starting from the most severe) FATAL, ERROR, WARN, INFO, DEBUG, and TRACE. Log4J also allows us to dynamically (through a configuration file) filter logs below a certain level. This way we can generate logs only for events that have a priority of WARN or higher and turn on the lower levels when there is a problem, due to which we want to see all the generated log statements.

This tutorial on JBoss does a very good job of explaining logging conventions in JBoss. I have excerpted the part that explains different logging levels below.

FATAL - Use the FATAL level priority for events that indicate a critical service failure. If a service issues a FATAL error it is completely unable to service requests of any kind.
ERROR - Use the ERROR level priority for events that indicate a disruption in a request or the ability to service a request. A service should have some capacity to continue to service requests in the presence of ERRORs.
WARN - Use the WARN level priority for events that may indicate a non-critical service error. Resumable errors, or minor breaches in request expectations fall into this category. The distinction between WARN and ERROR may be hard to discern and so its up to the developer to judge. The simplest criterion is would this failure result in a user support call. If it would use ERROR. If it would not use WARN.
INFO - Use the INFO level priority for service life-cycle events and other crucial related information. Looking at the INFO messages for a given service category should tell you exactly what state the service is in.
DEBUG - Use the DEBUG level priority for log messages that convey extra information regarding life-cycle events. Developer or in depth information required for support is the basis for this priority. The important point is that when the DEBUG level priority is enabled, the JBoss server log should not grow proportionally with the number of server requests. Looking at the DEBUG and INFO messages for a given service category should tell you exactly what state the service is in, as well as what server resources it is using: ports, interfaces, log files, etc.
TRACE - Use TRACE the level priority for log messages that are directly associated with activity that corresponds requests. Further, such messages should not be submitted to a Logger unless the Logger category priority threshold indicates that the message will be rendered. Use the Logger.isTraceEnabled() method to determine if the category priority threshold is enabled. The point of the TRACE priority is to allow for deep probing of the JBoss server behavior when necessary. When the TRACE level priority is enabled, you can expect the number of messages in the JBoss server log to grow at least a x N, where N is the number of requests received by the server, a some constant. The server log may well grow as power of N depending on the request-handling layer being traced.

Discuss this post in the learning forum.

Commercial Links



Note: This text was originally posted on my earlier blog at http://www.adaptivelearningonline.net

Comments

Popular posts from this blog

Running your own one person company

Recently there was a post on PuneTech on mom's re-entering the IT work force after a break. Two of the biggest concerns mentioned were : Coping with vast advances (changes) in the IT landscape Balancing work and family responsibilities Since I have been running a one person company for a good amount of time, I suggested that as an option. In this post I will discuss various aspects of running a one person company. Advantages: You have full control of your time. You can choose to spend as much or as little time as you would like. There is also a good chance that you will be able to decide when you want to spend that time. You get to work on something that you enjoy doing. Tremendous work satisfaction. You have the option of working from home. Disadvantages: It can take a little while for the work to get set, so you may not be able to see revenues for some time. It takes a huge amount of discipline to work without a boss, and without deadlines. You will not get the benefits (insuran

Some thoughts on redesigning education

Some time back I read a blog post on redesigning education. It asked some very good questions. Stuff which I had been thinking of myself. I left my thoughts on the blog, but I would also like to start a conversation around these ideas with those who read this blog as well. I would like to know what other people think of the issue of redesigning (college) education. I have often thought about how college education can be improved. To answer this question, we first have to ask a very basic question. What is the purpose of education? To me, we need education for 3 things: To learn more about the world around us To lead positive constructive lives To earn a good living / fulfill our ambitions I think education has to a large extent evolved to fulfill #3 (with a bias towards earning a comfortable living). The semester system, along with multiple choice tests, and grading, has made our education system into an assembly line. Students are pushed into the assembly line, given classes, admini

Testing Groovy domain classes

If you are trying to test Grails domain class constraints by putting your unit test cases in the 'test/unit' directory, then your tests will fail because the domain objects will not have the 'valdate' method. This can be resolved in two ways: Place the test cases inside test/integration (which will slow things down) Use the method 'mockForConstraintsTests(Trail)' to create mock method in your domain class and continue writing your test cases in 'test/unit' What follows is some example code around this finding. I am working on a Groovy on Grails project for a website to help programmers keep up and refresh their skills. I started with some domain classes and then moved on to write some unit tests. When we create a Grails project using grails create-app , it creates several directories, one of which is a directory called 'test' for holding unit tests. This directory contains two directories, 'unit', and 'integration' for uni