Performance Evaluation of Extended Storage Architectures for Transaction Processing

The use of non-volatile semiconductor memory within an extended storage hierarchy promises significant performance improvements for transaction processing. Although page-addressable semiconductor memories like extended memory, solid-state disks and disk caches are commercially available since several years, no detailed investigation of their use for transaction processing has been performed so far. We present a comprehensive simulation study that compares the performance of these storage types and of different usage forms. The following usage forms are considered: allocation of entire log and database files in non-volatile semiconductor memory, using a so-called write buffer to perform disk writes asynchronously, and caching of database pages at intermediate storage levels (in addition to main memory caching). Our simulations are conducted with both synthetically generated workloads and traces from real-life database applications. In particular, simulation results will be presented for the debit-credit workload frequently used in transaction processing benchmarks. As expected, the greatest performance improvements (but at the highest cost) can be achieved by storing log and database files completely in non-volatile semiconductor memory. For update-intensive workloads, a limited amount of non-volatile memory used as a write buffer also proved to be very effective. To reduce the number of disk reads; caching of database pages in addition to main memory is best supported by an extended memory buffer. In this respect, disk caches are found to be less effective as they are designed for one-level caching. Different storage costs suggest that it may be cost-effective to use two or even three of the intermediate storage types together. The performance improvements obtainable by the use of non-volatile semiconductor memory is also found to reduce the need for sophisticated DBMS buffer management in order to achieve high transaction processing performance