Re: backup of offline dropped datafile
> From the scenario that Koen described, it doesn't look that storage been
> allocated for any objects in the dropped data file, so queries against
> shoudn't fail.
If there is any table/index segment which had it's segment header block in
the offline datafile, most queries against it will definitely fail
(exceptions would be accessing table using ROWID access path or a cluster
access, which doesn't have to read segment header).
Index root blocks are always immediately next to segment header block, so
indexe scans would fail.
I don't have access to an Oracle DB right now, but you could try to allocate
extents to a table in your USERS tablespace to see whether it will hit a
"file inaccessible" error or not. It used to, but could be changed in later
versions (although I don't really why Oracle would do that, because an
offline drop renders tablespace physically invalid and it's only mean is
getting rid of a corrupt/lost datafile, followed by drop tablespace).
> Even if you recreate controlfiles/resetlogs (from backup or from trace),
> offline datafile will still apear in v$datafile - there is nothing you can
> about it - but from my understanding it should not cause any issue.
See above, offline drop renders tablespace invalid, everything done in the
tablespace after it is hacking.