Integer 

Static 

Derived: CPU_COUNT/2 

1 to either (CPU_COUNT x 2 x 3) or (DB_BLOCK_BUFFERS/50), whichever is less 

DB_BLOCK_LRU_LATCHES specifies the maximum number of LRU latch sets. The buffers of a buffer pool are equally divided among the working LRU latch sets of the buffer pool so that each buffer is protected by one LRU latch. Normally, the more latches you specify, the less contention exists for those latches. However, too many latches may result in small LRU lists, potentially reducing the cache life of a database block. The maximum of (CPU_COUNT x 2 x 3) ensures that the number of latches does not exceed twice the product of the number of CPUs and the number of buffer pools.  

Typically you should set this parameter to the number of CPUs or a multiple of that number. Each working set is handled entirely by one database writer (DBWn) process. Therefore, if multiple DBWn processes are running, the number of LRU latches should be greater than or equal to the number of DBWn processes. To balance the load evenly between the DBWn processes, the number of LRU latches in each buffer pool should be a multiple of the number of DBWn processes.

If you do not set this parameter, Oracle uses the value CPU_COUNT/2. This value is usually adequate. Increase this value only if misses are higher than 3%, as calculated from values in V$LATCH. When you increase the value, Oracle decides whether to use this value or reduce it based on a number of internal checks.  

See Also: Oracle8i Designing and Tuning for Performance for more information on setting this parameter.