Patent ID: 7693816
Filing Date: 2010-04-06
Classification: G06F

Abstract:
1. A computer system comprising: a storage system having a plurality of physical disk devices for storing data of a database and a control unit in data communication with a cache memory for prefetching data; a plurality of first computers coupled to the storage system and configured to access the database; and a second computer coupled to the first computer and the storage system and configured to execute a prefetch operation of some of the data of the database; wherein each of the first computers is further configured to: monitor a status of the prefetch operation for the second computer, measure a prefetch access time if the status is monitored as normal, measure a normal access time including the time to access data from the cache memory or the time to access data from the physical disk devices if the status is monitored as abnormal, store a cost management table which stores I/O cost information of each of logical volumes in the storage system, the I/O cost information is a value which results from converting the prefetch access time and the normal access time, receive, from a client computer, a query for accessing the database, generate an access plan related to the database on the basis of the query and the cost management table, access the database according to the generated access plan if the status is monitored as abnormal, and send the generated access plan to the second computer for prefetching if the status is monitored as normal, wherein the second computer is further configured to: measure a response time which is time from sending a prefetch command to the storage system to receiving a completion response of the prefetch command from the storage system, store a response time management table indicating a first threshold time and a second threshold time, which is less than the first threshold time, and manage change of the I/O cost information in the cost management table stored in each of the first computers if the response time is greater than the first threshold time, then manage change of the I/O cost information if the response time is less than the second threshold time.