Instance Architecture Enhancements In 12.2(12c R2)

Instance Architecture Enhancements In 12.2(12c R2)

From Oracle Database 12c Release 2 (12.2), read-only and read/write instances can co-exist within a single database. It supports for read/write and read-only instances in the same database. As we know that every database instance is either read/write or read-only.

Read-Only Instances

Read-only instances improve scalability of parallel queries for data warehousing workloads.

Read-only database instance can process queries, but does not support modification DML (UPDATE, DELETE, INSERT, and MERGE) or direct client connections.

Example

In an INSERT … SELECT statement, the read/write and read-only instances process the SELECT, whereas only the read/write instances process the INSERT.

To designate an instance as read-only, set the INSTANCE_MODE initialization parameter to READ_ONLY.

The default value of the parameter is READ_WRITE

Read-only instances have the following characteristics:

Can only open a database that has already been opened by a read/write instance.

Disable many background processes, including the checkpoint and archiver processes.

Can mount a disabled redo thread or a thread without any online redo log.

Read/Write Instances

A read/write database instance, which is the default, can process DML and supports direct connections from client applications.

Conclusion

Both read/write and read-only instances can open the same database.

This configuration is useful for parallel SQL statements that both query and modify data, because both read/write and read-only instances can query, while the read/write instances modify.

Cheers!!!!

With Best Wishes!!!!

Ahmad

Oracle Consultant

OCE (11gR2 RAC)

OCP (11gR2/10gR2/9iR2)

OracleRide Team!!!!

Reference-: Oracle Documentation