hi,
thanx hany, u gave the answer for when to take a tablespace offline and what happens when u take a tablespace offline.

but my doubt is, i took a tablespace offline which contains a table, i cached that table(using 'alter table cache
usually,when you give a select query, oracle searches for the table in buffer, and if it finds the table in buffer, it gives you the result..,but why it is accessing the disk when the table is cached.