Oracle8i Reference
Release 2 (8.1.6)

Part Number A76961-01





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Initialization Parameters, 28 of 188


Parameter type: 


Parameter class: 


Default value: 

Derived: 48 MB / DB_BLOCK_SIZE 

Range of values: 

4 to an operating system specific maximum 

Oracle Parallel Server: 

Multiple instances can have different values, and you can change the values as needed. 

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" pool and the "recycle" 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"_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, the values defaults to 1. 

This parameter affects the probability of data block pinging when Oracle Parallel Server is enabled: the more buffers, the more chance of pinging.  

Note: The checkpoint process is enabled automatically if the system configuration is such that moving checkpoint processing from the logwriter to a separate process is deemed to improve performance. Currently, the criteria are DB_FILES >= 50 or DB_BLOCK_BUFFERS >= 10000. 

See Also:


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