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Oracle Database Tips by Donald Burleson |
Oracle10g Grid Computing
with RAC
Chapter 7 - Cache Fusion and
Inter Instance Coordination
Shared Pool and Large PoolThe shared pool segment of the SGA contains three major areas: the
library cache, the dictionary cache, and buffers for parallel
execution messages.
Library Cache - The library cache includes the shared SQL
areas, private SQL areas (in shared server), PL/SQL procedures and
packages, and control structures such as library cache handles,
locks, synonym translations, and dependency tracking information. It
contains parse trees and execution plans for shareable SQL
statements, as well as pseudo code for PL/SQL program units. All
users access the shared SQL areas.Dictionary Cache - Includes the usernames, segment
information, profile data, tablespace information, and the sequence
numbers. The dictionary cache also contains descriptive information
or metadata about the schema objects. Oracle uses this metadata when
parsing SQL cursors or during the compilation of PL/SQL programs. The dictionary cache is also known as the row cache because it holds
the data in rows instead of buffers. It also holds entire blocks of
data. This helps to reduce physical access to the data dictionary
tables from the system tablespace, and also enables fine-grained
locking of individual data dictionary rows.
The large pool is an optional area. If the large_pool_size parameter
is set, then the large pool is configured as a separate heap within
a variable area of the SGA. The large pool is not a part of the
shared pool.Using the large pool instead of the shared pool decreases
fragmentation of the shared pool. Unlike the shared pool, the large
pool does not have an LRU list. Oracle does not attempt to age
memory out of the large pool.
The above text is
an excerpt from:
Oracle 10g Grid & Real Application
Clusters
Oracle 10g
Grid
Computing with RAC
ISBN 0-9744355-4-6
by Mike Ault, Madhu Tumma
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