LOG_BUFFER
specifies the amount of memory (in bytes) that Oracle uses when buffering redo entries to a redo log file. The parameter that needs to be configured for automatic shared memory management is the SGATARGET initialization parameter. In Oracle 10g, the SHAREDPOOLSIZE, LARGEPOOLSIZE, JAVAPOOLSIZE and DBCACHESIZE are known as the auto-tuned SGA parameters. LOGBUFFER=16M The above parameters can be replaced with SGATARGET = 256 M + 512M + 256 M + 16M + 16 M (fixed SGA overhead) = 1056 M Automatic Shared Memory Management may also be enabled dynamically. If you are using Enterprise Manager, you can enable SGA tuning by clicking the enable button on the SGA screen in the Memory Parameters section. Nov 10, 2005 Auto tuned SGA parameters dbcachesize sharedpoolsize largepoolsize javapoolsize These parameters are called auto tuned because automatic shared memory managment can dynamically change the sizes of these pools if it is enabled. DBCACHESIZE The value of this parameter affects the size of the SGA: It sets the default buffer pool. According to metalink note.
Property | Description |
---|---|
Parameter type | Big integer |
Default value | 2 MB to 32 MB, depending on the SGA size and CPU count |
Modifiable | No |
Modifiable in a PDB | No |
Range of values | 2 MB to operating system-dependent |
Basic | No |
Redo log entries contain a record of the changes that have been made to the database block buffers. The LGWR process writes redo log entries from the log buffer to a redo log file.
The log buffer size depends on the number of redo strands in the system. One redo strand is allocated for every 16 CPUs and has a default size of 2 MB. Oracle allocates a minimum of 2 redo strands per instance. When the log buffer size is not specified, any remaining memory in the redo granules is given to the log buffer.
See Also:
- Your operating system-specific Oracle documentation for the default value and range of values
- Oracle Streams Replication Administrator's Guide for information on using this parameter in an Oracle Streams environment
- Oracle Database Performance Tuning Guide for information on resizing the redo log buffer using this parameter
Automatic shared memory management simplifies the configuration of the SGA by automatically distributing the memory in the SGA for the following memory pools:
- Database buffer cache (default pool)
- Shared pool
- Large pool
- Java pool
- Streams pool
Automatic shared memory management is controlled by the
SGA_TARGET
parameter. Changes in the value of the SGA_TARGET
parameter automatically resize these memory pools. If these memory pools are set to nonzero values, then automatic shared memory management uses these values as minimum levels. Oracle recommends that you set the minimum values based on the minimum amount of memory an application component requires to function properly.The following memory caches are manually-sized components and are not controlled by automatic shared memory management:
- Redo log bufferThe redo log buffer is sized using the
LOG_BUFFER
initialization parameter, as described in 'Configuring the Redo Log Buffer'. - Other buffer caches (such as
KEEP
,RECYCLE
, and other nondefault block size)TheKEEP
pool is sized using theDB_KEEP_CACHE_SIZE
initialization parameter, as described in 'Configuring the KEEP Pool'.TheRECYCLE
pool is sized using theDB_RECYCLE_CACHE_SIZE
initialization parameter, as described in 'Configuring the RECYCLE Pool'. - Fixed SGA and other internal allocationsFixed SGA and other internal allocations are sized using the
DB_nK_CACHE_SIZE
initialization parameter.
The memory allocated to these memory caches is deducted from the value of the
SGA_TARGET
parameter when automatic shared memory management computes the values of the automatically-tuned memory pools.![Auto-tuned Auto-tuned](/uploads/1/2/6/1/126171851/131608081.jpg)
The following sections describe how to access and set the value of the
SGA_TARGET
parameter:See Also:
Log_buffer Is An Auto-tuned Parameter Number
- Oracle Database Concepts for information about the SGA
- Oracle Database Administrator's Guide for information about managing the SGA
- Oracle Database Administrator's Guide for information about using initialization parameters