thanks so fast responses.

I have 7 tablespaces: data, index, rbs, system, temp, tools, and users.

all I need is (trun off 3 tbs):
alter tablespace data read only;
alter tablespace index read only;
alter tablespace users read only; (most user default tbs)
I should keep other tbs in read write mode so user still can query. is that correct?
(I assume at least use need temp to sort, if temp be read only, the big query does not work)

or only (turn off 1 tbs)
alter tablespace rbs read only;
since all update activities can not write to rollback seg, user only can do query

am I correct?