Oracle DataGuard

Question

Oracle DataGuard is a technique to replicate data stored in an Oracle RDBMS across several Oracle engine instances. I'm wondering whether DataGuard really provides a linear scalability for a RDBMS. Do you have any experiences with the DataGuard? How does it behave under heavy load conditions?

Answer 1

DataGuard is typically used for business continuity, i.e. to have a failover database when the primary is unavailable. If you're looking for scalability, then you want RAC (Real Application Clusters), where multiple instances on separate hosts mount and share the same set of database files.

Generally, RAC scales out if you have a well-designed (db-centric) application that is bound by database host memory and CPU limitations.

Answer 2

We don't need instantaneous failover at our installation, so we use a DataGuard physical standby database on a separate server. It works by shipping archive log data over TNS to the physical standby and for our environment (not particularly heavy) it works fine. We typically have 1-10 log switches (57Mb log files) an hour and the standby has no problem keeping up.

It's not what you're asking about but there is an issue with logical standby databases and using Oracle auditing of sessions - you need 10.2.0.4 minimum with some exclusion logic to keep the audit records out of the standby else it can't keep up.