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Using Read-Only Tablespaces
Oracle Tips by Burleson Consulting |
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.
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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.
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