redo thread

今天学习了 oracle redo logs 里面有一个概念redo thread Redo Threads 1、选自官方文档 [quote] When speaking in the context of multiple database instances, the redo log for each database instance is also referred to as a redo thread. In typical configurations, only one database instance accesses an Oracle Database, so only one thread is present. In an Oracle Real Application Clusters environment, however, two or more instances concurrently access a single database and each instance has its own thread of redo. A separate redo thread for each instance avoids contention [color=red](竞争)[/color]for a single set of redo log files, thereby eliminating a potential performance bottleneck. [/quote] 2、选自网上的一个解释 ［quote］ in the rac system, each instance has to have its own redo log groups. the redo log file groups of an instance are collectively called a 'thread'. or more appropriately, a 'redo log thread'. Each instance has hits own redo thread. The redo log groups function in a true circular fashion; as one fills up, another redo log records the redo entries. in a stand-alone instance, there is only one thread. in a RAC system, typically you have as many threads as instances. The thread number identifies each thread.The threads may have different numbers of redo groups.but each group must have at least two members. [/quote] 大概意思就是 如果在典型的一个database对应一个instance的情况下，只有一个redo thread，但是 如果在rac环境下，一个database又多个instance，每个instance都有自己的redo log groups,每个instance的这些redo log files groups 就称为一个thread。 GROUP# THREAD# SEQUENCE# ARCHIVED STATUS ---------------------- ---------------------- ---------- -------- ---------------- 1 1 41 YES INACTIVE 2 1 42 YES INACTIVE 3 1 43 NO CURRENT