There is a new module I'd like to introduce called Debug.Rapidlog. When you inherit it, it overrides werror(), and allows for logging that interferes minimally with timing (it logs into a buffer, which then is emptied from a different thread at idle times).
The idea behind this module is that it allows logging timing sensitive code. I find that when I add logging to (e.g. pgsql) to chase rare bugs, the logging itself often causes the nature of the bug to change (or disappear).
Any objections/suggestions? I committed it to 8.1 for now, but I need the module in 8.0 as well eventually, since I have to run it in production systems at times. So please also evaluate fitness for inclusion in 8.0 (no rush though, it does not need to be in the latest release).