Real-time data cache size adjustment in a server computer

Claim 1

A method of operating a data cache, comprising the steps of: initializing a flag variable OK -- TO -- INCREASE to TRUE; periodically determining a moving average hit ratio R avg for the data cache over a first number of preceding periods; for the following cases of the determined value of R avg , performing the corresponding steps as follows: 0≦R avg ≦50%: if the size of the data cache is less than a maximum size S max , then increasing the number of buffers in the data cache to the lesser of twice the number of buffers in the cache during the present period and a maximum number N ht of buffers contained in the data cache when the data cache size is S max ; 50%<R avg ≦80%: (a) determining the data cache hit ratio for each of a second number of preceding periods; (b) setting the OK -- TO -- INCREASE flag to FALSE if the hit ratio over the second number of preceding periods has not substantially changed; (c) setting the OK -- TO -- INCREASE flag to TRUE if the hit ratio has decreased over any of the second number of preceding periods; (d) if the OK -- TO -- INCREASE flag is TRUE and the size of the data cache is less than S max , then increasing the number of buffers in the data cache to the lesser of 1.25 times the current number of buffers and N ht ; 80%<R avg ≦90%: (a) determining the data cache hit ratio for each of a third number of preceding periods; (b) setting the OK -- TO -- INCREASE flag to FALSE if the hit ratio over the third number of preceding periods has not increased monotonically; (c) setting the OK -- TO -- INCREASE flag to TRUE if the hit ratio has decreased over any of the third number of preceding periods; (d) if the OK -- TO -- INCREASE flag is TRUE and the size of the data cache is less than S max , then increasing the number of buffers in the data cache to the lesser of 1.10 times the current number of buffers and N ht ; and 90%<R avg ≦100%: leaving the number of buffers in the data cache unchanged.

Claim 2

A method of operating a data cache, comprising the steps of: initializing a flag variable OK -- TO -- INCREASE to TRUE; periodically determining a moving average hit ratio R avg for the data cache over a first number of preceding periods; for the following cases of the determined value of R avg , performing the corresponding steps as follows: 0≦R avg ≦50%: if the size of the data cache is less than a maximum size S max , then increasing the number of buffers in the data cache to the lesser of twice the number of buffers in the cache during the present period and a maximum number N ht of buffers contained in the data cache when the data cache size is S max ; 50%<R avg ≦80%: (a) determining the data cache hit ratio for each of a second number of preceding periods; (b) setting the OK -- TO -- INCREASE flag to FALSE if the hit ratio over the second number of preceding periods has not substantially changed; (c) setting the OK -- TO -- INCREASE flag to TRUE if the hit ratio has decreased over any of the second number of preceding periods; (d) if the OK -- TO -- INCREASE flag is TRUE and the size of the data cache is less than S max , then increasing the number of buffers in the data cache to the lesser of 1.25 times the current number of buffers and N ht ; 80%<R avg ≦90%: (a) determining the data cache hit ratio for each of a third number of preceding periods; (b) setting the OK -- TO -- INCREASE flag to FALSE if the hit ratio over the third number of preceding periods has not increased monotonically; (c) setting the OK -- TO -- INCREASE flag to TRUE if the hit ratio has decreased over any of the third number of preceding periods; (d) if the OK -- TO -- INCREASE flag is TRUE and the size of the data cache is less than S max , then increasing the number of buffers in the data cache to the lesser of 1.10 times the current number of buffers and N ht ; and 90%<R avg ≦100%: leaving the number of buffers in the data cache unchanged.