e—B^＋树：面向多用户数据库系统优化的索引技术

e-B￣+ -TREE:AN INDEXING ORGANIZATION OPTIMIZED FOR DBMS SUPPORTING MULTI-USERS

Ｂ＋树在数据库系统中已成为一种标准的索引结构，其上的并发控制机制对多用户数据库系统的性能有很大的影响．本文提出了一种变种Ｂ＋树──弹性Ｂ＋树－ｅ—Ｂ＋树（ｅｌａｓｔｉｃＢ＋－ｔｒｅｅ），定义了其上的安全点和操作及并发控制方法，对ｅ—Ｂ＋树的重构时机也进行了调整，降低了ｅ—Ｂ＋树上结点的合并／分裂频率，减少了ｅ—Ｂ＋树的维护开销，也缩短了封锁时间，从而使得其上操作的并发度和系统的效率得以提高．

B+ -trees are considered standard organization for indexes in database systems. The concurrent control mechanism on B+ -trees has a great effect on the performance of DBMS supporting multi-users. A variant of B+ -tree called e-B+ -tree(elastic B+ -tree) is presented in this paper. Then, the safe nodes and operations on e--B+ trees are defined and the moment of reconstruction of e-B+tree is regulated. All these measures not only reduce the overhead for maintaining the e--B+ tree and the time spent on locking, but also decrease the frequency of splitting and catenating operation. Therefore, the degree of concurrency of operations on e-B+tree and efficiency of the database system can increase by a big margin.