Database Reference
In-Depth Information
Within whole Database Buffer Cache, there lie three different
types of buffers or in other words three different states of
buffers. These three states are, Dirty Buffers, Free Buffers and
Pinned Buffers. Buffers that needs to be written to the data files
are marked dirty and hence got the name Dirty Buffers. Once
written to the data files they are available to be over-written or
those, which never had any data, are called Free Buffers. Buffers
that are currently being accessed or those that are explicitly
marked for future use, are called Pinned Buffers e.g. KEEP
buffer pool.
Redo Log Buffer Cache holds the information about the changes
that are being made to the database. Any change that you or
connected users make using any DML (INSERT, UPDATE,
DELETE) or DDL (CREATE, ALTER, DROP) statement will
get recorded in this part of the RAM or in other words SGA. The
parameter that determines the size of Redo Log Buffer is
LOB_BUFFER.
Large Pool is the optional area of SGA and can be requested as
needed. Its size can be adjusted using LARGE_POOL_SIZE
parameter inside init.ora file and can be dynamically altered
using ALTER SYSTEM statement. Large Pool is optionally
required for specific database operation like backup or restore to
avoid contention with rest of the good stuff of SGA.
Java Pool is another optional area and can be requested to
provide memory for java objects within Oracle database. Ever
since Sun Microsystems's collaboration with Oracle, we can
now create and store pre-complied Java programs as database
objects within the Oracle database and are treated the way other
objects are treated inside the database e.g. Java object created by
you or in other words under you schema will not be accessible to
anyone else unless you grant access.
The Non-Shared part of memory is called PGA (Program Global
Area) and contains the data and control information for a server
process. The information in PGA depends on the server
configuration. Oracle can be configured to run as dedicated
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