A key requirement of loggers is to stay out of the way when not needed
- that is, not to slow things down.  Java's log4j fulfills this
admirably.

Unlike in Java, where the initial overhead is one time only and hence
minimal, PHP's overhead is constantly repeated froms scratch, due to
the fact that each PHP request is in its own little world.  I measured
about 0.15 sec of CPU time (AMD 3000) to
parse the classes and run a logger, even with all the appenders shut
off.  On a busy server, that can add up to be a lot.  Although I'd
much rather use log4php than my current (feeble) logging system, our
boxen can't afford that much overhead *for every request*.

Any ideas?

(yes, I have thought about php accelarator and the like, and plan to
look into it - but the problem is still of general interest)