This section reports the number of buffers placed in cache following the fetch-and-discard (MRU) or normal (LRU) caching strategies:
“Cached(LRU) Buffers” reports the number of buffers that used normal cache strategy and were placed at the MRU end of the cache. This includes all buffers read directly from disk and placed at the MRU end, and all buffers that were found in cache. At the completion of the logical I/O, the buffer was placed at the MRU end of the cache.
“Discarded (MRU) Buffers” reports the number of buffers that were placed at the wash marker, using the fetch-and-discard strategy.
If you expect an entire table to be cached, but you e see a high value for “Discarded Buffers,” use showplan to see if the optimizer is generating the fetch-and-discard strategy when it should be using the normal cache strategy.
See “Specifying the cache strategy” on page 45 in Performance and Tuning: Optimizer for more information.
