(RAC) Real Application Clusters

Databases

Oracle

Oracle Database Features

Grid Infrastructure

Oracle Clusterware

Do you need RAC?

Using RAC where you don't have OJVM installed mostly gives you zero downtime patching (but there will be exceptions).
RAC is also a solution for scaling out (adding more smaller servers) when scaling up (making your big server bigger) is not an option.
Many other features of RAC can be achieved with less cost and complexity using Data Guard.
Virtualisation can also work well, but does introduce license complexity.

Retains the shared disk element of RAC but enables failover to a, started on demand, second instance instead of running multiple instances concurrently.
Licensable option, but is cheaper than full RAC. (RAC is $23,000 per core, RAC One-Node is $10,000 per core - Jun-2023)

Oracle Licensing & Support

srvctl -V

crsctl query crs softwareversion

crsctl check cluster

NOTE: crs_stat is deprecated since 12.1

crs_stat -t

crs_stat -u

Assumes CRS home directory is in your PATH. e.g. /u01/app/crs/product/11.1.0/crs/bin

sqlplus / as sysdba

SHOW PARAMETER cluster_database;

SHOW PARAMETER cluster_database_instances

SHOW PARAMETER cluster_interconnects