MRU (fetch-and-discard) is most often used for queries where a page is needed only once by the query, including:
Most table scans in queries that do not use joins
One or more tables in a join query
MRU replacement strategy is used for table scanning on heap tables. This strategy places pages into the cache just before the wash marker, as shown in Figure 2-3.
Figure 2-3: MRU strategy places pages just before the wash marker
Placing the pages needed only once at the wash marker means they do not push other pages out of the cache.
The fetch-and-discard strategy is used only on pages actually read from the disk for the query. If a page is already in cache due to earlier activity on the table, the page is placed at the MRU end of the cache.
Figure 2-4: Finding a needed page in cache
