Cache warming is designed to help reduce the execution times of the initial queries executed against a database. This is done by preloading the database server's cache with database pages that were referenced the last time the database was started. Warming the cache can improve performance only when the same query or similar queries are executed against a database each time it is started. However, if the statements executed at database startup are different than those executed the last time the database was started with cache collection on, cache warming does not improve performance.
You control the cache warming settings on the database server command line. There are two activities that can take place when a database is started and cache warming is turned on: collection of database pages and cache reloading (warming).
Collection of referenced database pages is controlled by the -cc database server option, and is turned on by default. When database page collection is turned on, the database server keeps track of every database page that is requested from database startup until one of the following occurs: the maximum number of pages has been collected (the value is based on cache size and database size), the collection rate falls below the minimum threshold value, or the database is shut down. The database server controls the maximum number of pages and the collection threshold. Once collection completes, the referenced pages are recorded in the database so they can be used to warm the cache the next time the database is started.
Cache warming (reloading) is turned on by default, and is controlled by the -cr database server option. To warm the cache, the database server checks whether the database contains a previously recorded collection of pages. If it does, the database server loads the corresponding pages into the cache. The database can still process requests while the cache is loading pages, but warming may stop if a significant amount of I/O activity is detected in the database. Cache warming stops in this case to avoid performance degradation of queries that access pages that are not contained in the set of pages being reloaded into the cache. You can specify the -cv option if you want messages about cache warming to appear in the database server messages window.
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