Application-controlled caching for web server

Focusing on the problem that under workloads of large dataset, the performance of a Web server is dropped due to the disk I/O blockings, an application-controlled caching (ACC) approach is presented. In ACC, the cache tracking module traces the status of file caches in kernel according to the files access process of applications, and cache replacement and prefetch are performed in cache control module to keep enough free space for file caches. With ACC, servers can control the file caches in user space, and determine whether a file is in caching, then schedule requests based on this to improve the parallelism of the processor and disk I/O. Meanwhile, servers can choose a suitable policy of caching and prefetching to increase cache hit ratio. ACC is implemented in Flash server as a demonstration, in which pyramidal selection scheme is adopted. Experiments show that the performance of Flash with ACC can be largely enhanced under workloads of a large dataset. Even when the dataset load is slightly larger than the physical memory space, its throughput is improved by about 24.4%; when the dataset load is 2-3 times larger, the throughput improved by 3-4 times.