1. Database Reference
  2. Initialization Parameters
  3. Initialization Parameters
  4. INSTANCE_MODE

1.142 INSTANCE_MODE

INSTANCE_MODE indicates whether the instance is read-write, read-only, or read-mostly.

Property Description

Parameter type

String

Syntax

INSTANCE_MODE = { READ-WRITE | READ-ONLY | READ-MOSTLY }

Default value

READ-WRITE

Modifiable

No

Basic

No

Oracle RAC

See the Oracle RAC restrictions in the initialization parameter description below.

A READ-WRITE instance is a regular Oracle instance.

A READ-ONLY instance is an Oracle instance that can only be opened in read-only mode.

A READ-MOSTLY instance is an Oracle instance that performs very few database writes.

These restrictions apply when setting the parameter on different Oracle Real Application Clusters (Oracle RAC) instances:

  1. There must be at least one instance alive with INSTANCE_MODE set to READ-WRITE at any given time. If the only instance with INSTANCE_MODE set to READ-WRITE goes down, all other instances will be brought down by Oracle automatically.

  2. An instance with INSTANCE_MODE set to READ-ONLY cannot be the first instance to open a database or any pluggable database (PDB) among all instances in an Oracle RAC cluster.

  3. Oracle does not support co-existence of an instance with INSTANCE_MODE set to READ-ONLY and an instance with INSTANCE_MODE set to READ-MOSTLY in the same Oracle RAC cluster.

Note:

This initialization parameter is available starting with Oracle Database 12c Release 2 (12.2.0.1).