jlog – jlog-Formatted Logging
jlog-formatted logs are binary logs with independent producers, which write the logs, and subscribers, which consume the logs. Momentum jlogs present themselves as directories in the filesystem.
Momentum produces jlogs in the following:
-
Aggregated cluster node logging (see “
ecelerity-cluster.confFile”) -
event_hydrant module used for tracking messages (see “event_hydrant – Message Tracking”)
-
Custom deployments configured to log data to jlog files for consumption by another application, such as Perl scripts. In turn, these scripts may push the data elsewhere, e.g.: to a database. (see “custom_logger – User-defined Logging”)
Warning
We expressly recommend against writing jlogs to an NFS file system because of concerns about its performance in general and its reliability, especially on Linux.
This module is loaded automatically as required and does not need to be explicitly included.
Warning
If your system is generating jlogs, ensure that they are being consumed. Otherwise, the /var/log/ecelerity partition will become exceedingly large.
The following executable commands are used for analyzing and maintaining jlog files:
Using the JLog::Reader module that ships with Momentum, you can read your jlog files with a Perl script. This module is found in the /opt/msys/3rdParty/lib/perl5/vendor_perl/5.16.3/x86_64-linux-thread-multi/JLog directory on any Momentum node.
A common use case is to process the jlog files created by a custom_logger module. In “custom_logger”, a jlog is created at /var/log/ecelerity/delivery_log_rt with a subscriber name my_subscriber.
custom_logger "custom_logger_jlog" {
# custom logging in jlog format
delivery_logfile = "jlog://var/log/ecelerity/delivery_log_rt=>my_subscriber"
delivery_format = "%t@%r@%R@%vctx_mess{customerid}"
}
You can read the jlog in the following way:
#!/opt/msys/3rdParty/bin/perl use JLog::Reader; my $path = "/var/log/ecelerity/delivery_log_rt"; my $subscriber = "my_subscriber"; my $reader = JLog::Reader->new($path); $reader->open($subscriber); while (my $line = $reader->read) { # Do something with $line such as process and push into a database } # If you're done with the various $line's or they were pushed to a db # successfully set a checkpoint. $reader->checkpoint(); # if you're done with reading the log, close it $reader->close();
This code opens a jlog and reads each line in that jlog. The $path and $subscriber variables should match those configured in the custom_logger module. The checkpoint method indicates that records have been read successfully to this point. Records are removed after they have been read by all registered subscribers.
For more information about JLog::Reader, issue the command /opt/msys/3rdParty/bin/perldoc JLog::Reader .