面向更新密集型应用的内存数据库高效检查点技术

面向更新密集型应用的内存数据库系统,其检查点技术应符合几个关键的要求,包括检查点操作对正常事务处理的干扰尽可能小、能够处理存取倾斜状况、支持数据库系统的快速恢复、提供恢复过程中的系统可用性等.该文提出一种事务一致的分区检查点技术,采用基于元组的动态多版本并发控制机制,避免了读写事务的加锁冲突,提高系统吞吐能力;检查点操作以只读事务形式实现,存多版本并发控制下,避免检查点操作对正常事务处理的堵塞;由于检查点文件是事务一致的,只需要记录事务的Redo 日志信息,在系统恢复过程中,只需要对日志文件进行一遍扫描处理,加快恢复过程;基于优先级的数据分区装载和恢复,使得恢复过程中新事务的数据存取请求迅速得到满足,保证了恢复过程中的系统可用性.由于采用两级版本管理机制以及动态版本共享技术,多版本管理的空间开销降低到可以接受的水平.实验结果表明,文中提出的检查点技术方案获得比模糊检查点技术高27%的系统吞吐量,同时版本管理的空间开销在可接受的范围之内,满足高性能应用的要求.

An Efficient Checkpointing Scheme for Update Intensive Applications in Main Memory Database Systems

Four requirements for checkpointing in update intensive main memory database sys-tems are identified, namely how checkpointing interferes with normal transaction processing, how checkpointing handles skewed access pattern, whether checkpointing supports fast restart, and whether checkpointing provides system availability during recovery. A partition based trans-action-consistent checkpoint scheme is proposed in this paper, the scheme uses a tuple-level dy-namic multi-versioning concurrency control protocol to avoid the lock conflicts between read only transactions and update transactions, thus achieves high system throughput. Checkpointing is implemented as data partition read only transactions, and incurs little interfering with normal transaction processing, furthermore transaction-consistent checkpoint requires writing out only redo log records of committed transactions, during recovery only one pass of log scanning is nee-ded. Priority-based on demand partition recovery gives high attention to data access demands of executing transactions, provides system availability during recovery, which is critical for high performance applications. Finally, two level version management and dynamic version sharing re-duce space overhead to an acceptable level. Experiment results demonstrate effectiveness and effi-ciency of the proposed scheme.