Optimistic Intra-Transaction Parallelism on Chip Multiprocessors

With the advent of chip multiprocessors, exploiting intra-transaction parallelism is an attractive way of improving transaction performance. However, exploiting intra-transaction parallelism in existing database systems is difficult, for two reasons: first, significant changes are required to avoid races or conflicts within the DBMS, and second, adding threads to transactions requires a high level of sophistication from transaction programmers. In this paper we show how dividing a transaction into speculative threads solves both problems—it minimizes the changes required to the DBMS, and the details of parallelization are hidden from the transaction programmer. Our technique requires a limited number of small, localized changes to a subset of the low-level data structures in the DBMS. Through this method of parallelizing transactions we can dramatically improve performance: on a simulated 4-processor chipmultiprocessor, we improve the response time by 36–74% for three of the five TPC-C transactions.