I wish we could move away from unclear log levels and sprintf argument mashing. Log4r is complete but it's design is inherited from a static world.
Something simple like console.log() makes it easy for the developer to add more context to the line because he doesn't have to think how he will represent the data or choose a log level.
I've been working on a similar solution in the ruby world. It's nearly stable API-wise and already running in production: https://github.com/zimbatm/lines-ruby
All the mentioned solutions are great!
I personally think it does not matter if we use key-value output or "sentences", they have to be parsed anyway. I prefer writing Function: Foo instead of fn=Foo, just because I think it's easier to read when a human actually has to dig into the raw logs. For machines it's really the same.
I will detail how I parse logs with Logstash in a future post of this series. (And some logs like apache / nginx / mysql cannot be changed to use key-value format easily, so you might not be able to get around string parsing anyway)
Log4r allows you to use a key-value format as well, just modify the PatternFormatter and your output (in the logger.rb in my example).
I'm a big fan of heroku's scrolls gem[1], it uses a key=value format and is intended to be streamed straight into stdout. We're using it with splunk storm[2] which automatically parses logs in the key=value format and from there you can slice/dice the logs using their query language and graphing. This makes it super easy to spot patterns in the logs where there might be an issue.
Yes Lines-ruby is similar to scrolls with richer data types and support for ActiveRecord and Rack loggers out of the box. It also provides the parser to extract the data back.
Something simple like console.log() makes it easy for the developer to add more context to the line because he doesn't have to think how he will represent the data or choose a log level.
I've been working on a similar solution in the ruby world. It's nearly stable API-wise and already running in production: https://github.com/zimbatm/lines-ruby