Basically, in this document, you can see that if your log buffer is too small, then you will find "log buffer space" wait events in V$SYSTEM_EVENT. If you have "log buffer space" wait events, consider increasing your log buffer. If the log buffer is too large, then the average wait time for the "log file sync" wait event (again, found in V$SYSTEM_EVENT) can become too large. When you increase the log buffer, monitor the average wait time for this event. If the average wait time increases significantly, then decrease your log buffer size.
This was first published in February 2005