Using Oracle�s Read-Only Tablespaces

In a busy environment where many different applications require access to a tablespace, it is sometimes desirable to use the read-only tablespace feature of Oracle 7.3. With read-only tablespaces, separate instance can be mapped to the same tablespaces, each accessing the tablespace in read-only mode. Of course, sharing a tablespace across Oracle instances increases the risk that I/O against the shared tablespaces may become excessive. As we can see in Figure 8.13, a read-only tablespace does not have the same overhead as an updatable tablespace.
Figure 8.13 Oracle read-only tablespaces.

This approach has several advantages:

* Buffer pool isolation--The foremost advantage is the isolation of the buffer pools for each instance that is accessing the tablespace. If user A on instance A flushes his buffer by doing a full-table scan, user B on instance B will still have the blocks needed in memory.

* Easy sharing of table data--Read-only tablespaces offer an alternative to table replication, and the update problems associated with replicated tables. Since a read-only tablespace may only be defined as updatable by one instance, updates are controlled at the system level.

If you like Oracle tuning, you may enjoy the book Oracle Tuning: The Definitive Reference , with over 900 pages of BC's favorite tuning tips & scripts.

You can buy it directly from the publisher and save 30%, and get instant access to the code depot of Oracle tuning scripts.