I get about 20% of "Other Wait" of which most of this is "unspecified wait" and the rest is "misc other wait". What things come under these categories?
Total time spent waiting for miscellaneous operations to complete. None of the underlying operations (wait events) can be classified into any other wait categories (usually negligible).
The 'Unspecified Event' is an oracle event (you can check by selecting from v$event_name) and we're just reporting a real event happening in Oracle-the Oracle documentation should have more info.
Additional info from Oracle...
Oracle Server - Enterprise Edition - Version: 184.108.40.206
This problem can occur on any platform.
V$session_wait shows null event but 10046 trace shows the correct wait event.
"null event" could appear in V$SESSION_WAIT in cases when no wait was specified or when the session is not actually waiting at all. With this fix "null event" now only means that the session is not waiting "unspecified wait event" is now used to indicate a wait state where no named event has been supplied.
Apply fix for BUG:2843192
Apply 9204 patchset
Upgrade to Oracle 10i