You effectively enable manual shared memory management by disabling both automatic memory management and automatic shared memory management. You must then set values for the various SGA components, as described in the following sections. Setting the Buffer Cache Initialization Parameters The buffer cache initialization parameters determine the size of the buffer cache component of the SGA.
You use them to specify the sizes of caches sga option the various block sizes used by the database. These initialization parameters are all dynamic.
Automatic Memory Management (AMM) in Oracle Database 11g Release 1
The size of a buffer cache affects performance. Larger cache sizes generally reduce the number of disk reads and writes.
However, a large cache may take up too much memory and induce memory paging or swapping. Oracle Database supports multiple block sizes in a database.
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If you create tablespaces with non-standard block sizes, you must configure non-standard block size buffers to accommodate these tablespaces. Legitimate values are from 2K to 32K. Note: Platform-specific restrictions regarding the maximum block size apply, so some of these sizes might not be allowed on some platforms.
The size of the cache of standard block size buffers is MB. The cache has a limited size, so not all the data on disk can fit in the cache. When the cache is full, subsequent cache misses cause Sga option Database to write dirty data already in the cache to disk to make room for the new data.
Using Automatic Shared Memory Management
sga option If a buffer is not dirty, it does not need to be written to disk before a new block can be read into the buffer. Subsequent access to any data that was sga option to disk and then overwritten results in additional cache misses. The size of the cache affects the likelihood that a request for data results in a sga option hit. If the cache is large, it is more likely to contain the data that is requested.
Increasing the size of a cache increases the percentage of data requests that result in cache hits. You can change the size of the buffer cache while the instance is running, without having to shut down the database. Multiple Buffer Pools You can configure the database buffer cache with separate buffer pools that either keep data in the buffer cache or make the difference between real and demo accounts available for new data immediately after using the data blocks.
Particular schema objects tables, clusters, indexes, and sga option can then be assigned to the appropriate buffer pool to control the way their data blocks age out of the cache.
The KEEP buffer pool retains sga option schema object's data blocks in memory. Note: Multiple buffer pools are only available for the standard block size. Oracle Database selects an appropriate default value.
Configuring Memory Manually
The internal SGA overhead refers to memory that is allocated by Oracle Database during startup, based on the values of sga option other initialization parameters. This memory is used to maintain state for different server components in the SGA. You must therefore set this parameter so that it includes the sga option SGA overhead in addition to the desired value for shared pool size.
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- The In-Memory Column Store does not replace the database buffer cache.
When migrating from a release that is earlier than Oracle Database 10g Release 1, the Oracle Database 11g migration sga option recommend a new value for this parameter based on the value of internal SGA overhead in the pre-upgrade environment and based on the old value of this parameter. When you use automatic shared memory management in Oracle Database 11g, the shared pool is automatically tuned, and an ORA error would not be generated. Therefore, if you expect to increase the maximum size of the result cache, take this into consideration when sizing the shared pool.
Using Manual Shared Memory Management
The large pool is an optional component of the SGA. Typically, there is no need to specify this parameter, because the default maximum size is chosen by the database based on total memory available to the SGA and on the memory management method currently in sga option.
In each case, the value is rounded up to the nearest multiple of 32K. FLUSH clears the result cache and releases all sga option memory back to the shared pool.
This parameter cannot be sga option in conjunction with automatic memory management or automatic shared memory management. These parameters are rarely used. On platforms that do not support this much physical memory, this parameter is ignored. See Also:.