参考文档：

Real Application Clusters Administration and Deployment Guide

3 Administering Database Instances and Cluster Databases

Initialization Parameter Use in Oracle RAC

Table 3-3 Initialization Parameters Specific to Oracle RAC

THREAD

Specifies the number of the redo threads to be used by an instance. You can specify any available redo thread number if that thread number is enabled and is not used. If specified, this parameter must have unique values on all instances. The best practice is to use the INSTANCE_NAME parameter to specify redo log groups.

 

Database Reference

1.350 THREAD

THREAD has been superseded by the INSTANCE_NAME and INSTANCE_NUMBER parameters, and will be made obsolete in a future release of the Oracle Database.

Property	Description
Parameter type	Integer
Default value	0
Modifiable	No
Modifiable in a PDB	No
Range of values	0 to the maximum number of enabled threads
Basic	No
Oracle RAC	If specified, multiple instances must have different values.

很久之前，看到一个数据库，是主备模式， RAC架构。

奇怪的是，发现RAC节点1上的Thread不是默认的1，是默认的0,节点2上thread是1.

备库是单实例的，thread居然是0.

当时就比较好奇。咨询了下现场的工程师，说这样没什么问题，已经运行几年了。dg之间的切换也没有什么问题。当时很纳闷，thread怎么和默认的不一样。

今天看到官方的文档的时候，恍然大悟，原来可以设置成不一样。

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