A special strategy keeps index pages in cache. Data pages make only a single trip through the cache: they are read in at the MRU end of the cache or placed just before the wash marker, depending on the cache strategy chosen for the query.
Once the pages reach the LRU end of the cache, the buffer for that page is reused when another page needs to be read into cache.
For index pages, a counter controls the number of trips that an index page can make through the cache.
When the counter is greater than 0 for an index page, and it reaches the LRU end of the page chain, the counter is decremented by 1, and the page is placed at the MRU end again.
By default, the number of trips that an index page makes through the cache is set to 0. To change the default, a System Administrator can set the number of index trips configuration parameter
For more information, see the System Administration Guide.