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Memory DBMS Theory

2009-09-17 13:27:48| 分类： dbms | 标签： |举报 |字号大中小订阅

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MMDB
   - All data are stored in main memory (Remove I/O bottleneck)
   - More than one copy of data
   - Synchronization between common DBMS and memory DBMS
Key technology
   - Data layout
   - Index selection
   - I/O management
   - Query and optimization
   - Concurrency control
   - Enhanced ACID
   - Enhanced Recoverability

高效内存结构技术
    MMDB直接通过内存指针访问数据库，因此没有了地址映射的时间
    影子内存（ShadowMemory）是MMDB的主拷贝（Primary DataBase）的一份"影子拷贝"。
    所有的更新操作都在SM中进行，且都记录在活动日志中（Active Log）。每当一个事务提交时，由他所产生的在SM中的"后映像"拷贝到PDB中。
高速缓存数据管理技术
    B-tree结构的主要目的是减少完成数据文件的索引查找所需要的磁盘I/O的数量
    内存索引的目标是减少整体的计算时间同时尽可能少地占用内存
    T-tree是针对主存访问优化的索引技术
    T-tree 本身不保存索引数据，由于所有数据都存放在主存，所以仅仅包含指向实际数据的指针域。
查询优化
    在MMDB可以确定所有的数据都在主存中
日志和恢复
    磁盘上的备份数据库主存数据库和备份数据库之间需要同步以保持数据的一致性

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