Do you want to easily control different events that may occure in your system? Are you boring of looking into log files (or do you reviewing them regularly?). Here’s simple method how to not miss any interesting event! Place logs on X server root!
As you can see you can mix logs from many sources. It’s “tail -f” ported to X server. Here’s command line invocation I placed in ~/.xinitrc:
root-tail -color white -font "-misc-*-*-r-*-*-10-*-*-*-*-*-*-*"\
-g 2020x350+1-10 \
--outline --minspace \
~/procmail.log \
/var/log/messages \
/var/log/daemon.log \
/var/log/syslog \
~/.xsession-errors \
&
Pretty useful small pgm. Enjoy!
Sometimes you want to customize logging level for given package in your application (to see tracing details for example). If you’re using commons-logging library the configuration file is called “commons-logging.properties” and it should be places somewhere on classpath.
org.apache.commons.logging.Log=org.apache.commons.logging.impl.SimpleLog
priority=1
Then we can configure SimpleLog back-end just declared in simplelog.properties:
org.apache.commons.logging.simplelog.defaultlog=warn
org.apache.commons.logging.simplelog.log.com.mycompany.package=debug
You place those two files on classpath, redeploy application and … NOTHING HAPPENS. Those files aren’t visible!
(more…)
Recently I observed that AdWords-generated traffic dissapeared from Analytics panel. I thought: WTH?
I checked the logs and saw that URL called by AdWords:
http://my-site.com/?gclid=342343445345....
Generated 403 (Forbidden) server response. That was caused by recent change in Lighttpd filtering rules. I was paying for AdWords traffic but customer hit 403 error page. Ops!
In order to easily spot such problems in future I created the following scanner to easily find all error server responses.
awk '$9>=400' /var/log/lighttpd/access.log | less
If you are boring of 404 errors you can filter them out as well (leaving only 403 / 500 errors for investigation):
awk '$9>=400 && $9 != 404' /var/log/lighttpd/access.log | less
I discovered that the following URLs were inaccessible:
- /robots.txt (exclusion rules for web crawlers)
- /favicon.ico (icon used by web browsers)
Next step could be automation of this check (cron job that will send an alert if errant responses count is higher than N). It’s left as exercise for the reader.
During recent 2nd level cache implementation research I noticed EHCache has a very funny dependency: slf4j. Hey, WTH, yet another log library implementation? – I asked myself. No commons-logging as everywhere?
I googled around and found “The evils of commons-logging.jar and its ilk” article. It highlight some problems related to commons-logging usage:
- Different commons-logging versions in one project mirrors DLL-hell problem
- Collection logs from all sources into one stream has no bigger value for a developer
- Advanced configuration is logging back-end dependant (appenders for log4j for example), so unified layer is not valuable here
- Configuration is not intuitive and hard
I agree with 1, 3 and 4. 2 is questionable: sometimes logs sorted in one timeline allows for better error analysis.
slf4j is proposed as an alternative. It’s more modular and (probably) simpler that commons-logging. All configuration is a matter of placing selected implementation (slf4j-jdk14-1.5.8.jar for instance) jar on classpath. And voila! – logging is done thru JDK 1.4 logging. Quite simple.
I bet everyone knows how to enable SQL logging for Hibernate. If you add this parametr to Hibernate configuration:
<property name="hibernate.show_sql">true</property>
you will see queries like this in log file:
select roles0_.EntityKey as Entity9_1_, roles0_.ENTITYKEY as ENTITY9_168_0_
from USERROLE roles0_
where roles0_.EntityKey=?
but wait: what value is passed as parameter by Hibernate? (parameters are marked as “?” in JDBC) You have configure TRACE level for some log categories, here’s example for simplelog.properties:
(more…)
