SOME IMPROVEMENTS OF SI IN OSCAR DBMS

摘要

Snapshot Isolation is a newly introduced multi-version concurrency control protocol not only avoids many of the common concurrency anomal ies but also gets a satisfying concurrency. Besides, it is convenient to implement SI. However, traditional SI has it's own foibles: it's inside policy named First-Commit-Winner may result in the rol I back of too many invalid operations and the waste of system resource; traditional SI can't avoid one kind of constraint violation anomaly named Write Skew. This article makes some improvements of SI : Fi rst, a First-Write-Winner policy instead of the First-Commit-Winner is given to improve the system performance. Second, some amendment is made to avoid the Wr ite Skew anomaly effecti vely. The improved SI has been implemented in OSCAR, which is our DBMS for engineering application.