Data Dictionary Cache
The second major cache area within the shared pool for Oracle
is the data dictionary cache.
As a key buffer cache of the shared pool, the data dictionary
cache houses the internal data structures for the Oracle database.
The data dictionary is accessed very often
by various Oracle processes. Dictionary Cache is the memory
areas designated to hold dictionary data. It is also known as
the row cache because it holds data as rows instead of buffers
(which hold entire blocks of data).
When an Oracle database is first started, no data exists in the
data dictionary cache. For this reason, the dictionary cache
should be monitored and tuned only after the Oracle 11g database
environment has been up and running for a period of time. One way
to minimize contention issues on the data dictionary cache is to
use Locally Managed Tablespaces (LMT) for Oracle 11g tablespaces
instead of dictionary managed tablespaces. This will help reduced
contention on the data dictionary cache.
The Data Dictionary Cache Misses Oracle metric
ratio of the number of data dictionary requests resulting in
cache misses. The data dictionary is used to hold metadata
(table and column names, etc. and is heavily referenced during
SQL pre-execution processing.)
are having difficulties regarding the data dictionary cache
Miss Percentage above is greater than 10-15, you may need to
tune your library cache usage by adding additional memory to the
data dictionary cache. Increasing memory is done by increasing
the SHARED_POOL_SIZE parameter in the INITsid.ora