The app my colleagues and I maintain has an Oracle database at the back-end. We’re looking at occasionally running the app in a ‘restricted’ mode with one of the database tablespaces set to read-only. We can easily move the necessary tables and indexes over to separate tablespaces which will be writable in ‘restricted’ mode. However, despite several Google searches I can’t determine in which tablespace Oracle stores sequences.
This answer mentions that sequence values are stored in the SYSTEM.SEQ$ table. I don’t have access to an Oracle DB right now, but I would guess that this table lives in one of the system tablespaces. The tablespace we are making read-only isn’t a system tablespace, it’s one of our own data tablespaces.
On a dev database I can successfully SELECT from a sequence with the relevant tablespace made read-only.
I suspect it won’t be a problem to have this tablespace read-only, but I’d rather my suspicions were confirmed by more than just ad-hoc experimentation. Could someone please enlighten me?
Sequences are (mostly) in SEQ$. Parts will be in OBJ$ (and grants elsewhere). But all these tables are in the SYSTEM tablespace. Some SYSTEM objects are in SYSAUX. DBA_SEGMENTS is a good view to identify which tablespaces an object (such as SEQ$) resides in.
I suspect that Oracle wouldn’t let you put these tablespaces into READ ONLY mode as, to do so, it would need to flag that tablespace as read only which is recorded in a SYSTEM table in that tablespace. Sort of like locking the key in the safe which it unlocks.