I. Features Introduced in Ingres II 2.5 : Large Cache Support
 
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Large Cache Support
In Ingres II 2.5, the total number of pages in all caches has been revised from an un-enforced limit of 65536 to 2**32-1. Ingres II 2.5 supports a 4 GB cache.
In previous releases, when those pages belonging to a specific table needed to be located, the buffer manager sequentially searched every buffer in every cache to find them. Even in installations with small caches, this was an expensive operation, especially in those frequent instances in which there were no table-pages in any cache. This operation occurred, for example, when a table's TCB was about to be released, typically when all referencing transactions had no immediate need to use the table. Delays caused by this operation could show up in unexpected situations, such as the use of statement level rules.
In Ingres II 2.5, a cross-cache table hash queue has been added to the buffer manager to which pages are added as they are faulted in and removed when they are tossed. Thus, when the need to know a table's pages arises, a hash on the table's database ID and table ID is made and that list searched for matching pages. This change results in a significant decrease in the number of cache pages visited and is most dramatic in installations configured with very large or multiple caches.