LRU Concurrency

For databases with an Enterprise license, two buffer pool tuning parameters provide the ability to ease contention on the buffer pool LRU latch by altering LRU replacement policy in both the primary and alternate buffer pools, with the goal of improving throughput performance. (See AlternateBuffer Pool for information on the Alternate Buffer Pool.)

The LRU skip parameters allow you to specify the number of times a buffer in the buffer pool is accessed before it is placed on the Most Recently Used (MRU) end of the LRU chain. Accessing a buffer a specified number of times eliminates the need to acquire the LRU latch each time a buffer is accessed.

Specifying the LRU skip parameters is helpful when high LRU latch wait timeouts are occurring (observable in PROMON or by VST). When the LRU skip value is tuned to your environment, contention on the LRU latch decreases, improving concurrency and performance, and there is no increase in the number of page misses in the buffer pool. If increasing the LRU skip value causes increased buffer pool misses, then the value should be tuned down or turned off altogether. Setting the LRU skip value to zero disables the feature, and is the default.

LRU skip values can be specified at startup through the startup parameters, -lruskips and -lru2skips, or they can be set and adjusted with PROMON or VST. They are not implemented for private buffer pool data access.

If you modify the value after startup, the change will not take effect on buffers currently in the buffer pool until the current value expires and the buffer is moved to the MRU end of the chain.