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Parameter type
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Integer
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Default value
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Derived: 48 MB / DB_BLOCK_SIZE
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Parameter class
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Static
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Range of values
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50 to an operating system-specific maximum
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Real Application Clusters
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Multiple instances can have different values, and you can change the values as needed.
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Note:
This parameter is deprecated in favor of the DB_CACHE_SIZE parameter. Oracle recommends that you use DB_CACHE_SIZE instead. Also, DB_BLOCK_BUFFERS cannot be combined with the new dynamic DB_CACHE_SIZE parameter; combining these parameters in the same parameter file will produce an error. DB_BLOCK_BUFFERS is retained for backward compatibility.
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DB_BLOCK_BUFFERS specifies the number of database buffers in the buffer cache. It is one of several parameters that contribute to the total memory requirements of the SGA of an instance.
This parameter, together with DB_BLOCK_SIZE, determines the total size of the buffer cache. Effective use of the buffer cache can greatly reduce the I/O load on the database. DB_BLOCK_SIZE can be specified only when the database is first created, so you use DB_BLOCK_BUFFERS to control the size of the buffer cache.
The buffers for the "keep" buffer pool and the "recycle" buffer pool come out of the buffer cache. In addition, each LRU list in the buffer cache must have at least 50 buffers. Therefore, if you specify BUFFER_POOL_KEEP and BUFFER_POOL_RECYCLE, be sure the value of DB_BLOCK_BUFFERS conforms to the following formula:
DB_BLOCK_BUFFERS > #_buffers_in_"keep"_buffer_pool
+ #_BUFFERS_IN_"recycle"_buffer_pool
+ 50*(DB_BLOCK_LRU_LATCHES
- #_lru_latches_in_"keep"_buffer_pool
- #_lru_latches_in_"recycle"_buffer_pool)
If you did not specify any LRU latches in BUFFER_POOL_KEEP and BUFFER_POOL_RECYCLE, then the values default to 1.
This parameter affects the probability of data block pinging when Oracle9i Real Application Clusters are enabled: the more buffers, the greater the chance of pinging.
