Patent ID: 7287144

Claim:
A hit ratio estimation device for estimating a hit ratio in a session data cache, in which a Web server sets up said session data cache of preset size for each Web application, reads said session data from said session data cache or a permanent store, depending on whether a cache hit for session data in said session data cache or a cache miss, and refers to or updates an attribute value of read data; wherein, a leave probability as the reciprocal of an average value of the number of data reading sessions per session is defined as p 1 , the time interval of data reading sessions adjacent to each other in a time axis direction within the same session is called a think time, the average value and variance of the think time are defined as m and s 2 , and the cache hit ratio for data reading sessions is defined as r; wherein, said Web server mounts one or more counters for counting predetermined count information capable of calculating p 1 , m, s 2 and r; wherein, one or more data reading sessions corresponding to one Web page transmission request within the same session are called a group of data reading sessions, and a first data reading session among said group of data reading sessions is called a first reading session of the group of data reading sessions, said hit ratio estimation device estimating the hit ratio ra in said session data cache only for the first reading session of said group of data reading sessions, said hit ratio estimation device comprising: a computational expression setting component adapted to set a computational expression f(a)=a (a on the left side is a substituted for original value, and a on the right is a as new value obtained from the left side computation) including p 1 , m, s 2 , r, p 1 a , ma and s 2 a , said computational expression for a fix point computing method having a variable a, in which the leave probability p 1 a , average value ma of think time and variance s 2 a of think time are defined only for the first reading session of said group of data reading sessions, and the average value of the number of data reading sessions included in the group of data reading sessions is defined as a; a true value searching component adapted to search an almost true value of a by the fix point computing method based on said computational expression f(a)=a; and a estimation component adapted to estimate ra based on a searched value of a.