Shadow Database for Hot Standby

Question

Hi,
Our company uses embedded Oracle10g Standard and Enterprise Editions. The Oracle database schemas drive real-time applications; such as VoIP, etc. We need to shadow our applications and Oracle database to a failover server.
We identified several methods to make and maintain a hot standby copy of an embedded Oracle database; including Data Guard, Oracle9i Replication, Streams, Recovery Manager, RAC, etc.
Can you recommend a light weight, easy to implement, low cost solutions to making and maintaining a shadowed Oracle10g database? The replication is one way, writing from the active database to the standby, without check points, roll backs or any other features.
Regards,
Bruce
LignUp Corporation

Answer 1

Bruce,
it looks to me that in order to satisfy the recovery time and affordable data loss requirements you could use either of two products - RAC or DataGuard.
1. The RAC - comes with Standard edition for free, comes with Enterprise Edition at extra cost (awkward, isn't it?)
pros -
will allow you automatically recover in matter of seconds from failure of the node with zero data loss. will allow you automatically distribute the workload among the clustered nodes.
cons - there is a single point of failure - the shared storage where cluster keeps the data.
Also you should purchase the additional Oracle database license for the second (third,..) cluster node. Well, not in every configuration. I belive if you use user-based licensing model then clustered configuration will be no different from single node configuration in terms of costs. If you use the CPU based licensing model - you can split your licenses among the clustered nodes - for example if you've purchased 4 CPU licenses you can install 2 node cluster with dual-CPU servers. You have to make sure that dual-CPU server will sustain the load in case of failure of one node. In this case to feel safer you can purchase quad-CPU servers , but allow Oracle to run only on two CPUs on each node - in case of failure just change the affinity mask of the oracle process to let it use the extra 2 CPUs.
2. DataGuard - comes with EntEd. at no extra cost, is not available with standard edition.
you can setup Dataguard for zero loss configuration. the switchover time - probably would be closer to minute than to 5 seconds
pros - doesn't require shared storage thus eliminates the single point of failure. does not require extra licensing costs - the second node is always in mounted state (unless you want to use it for read-only query processing).
cons - near real-time recovery (compared to real-time of RAC). Requires double storage (to keep the standby database). Requires the extra standby server which is not fully used in production until the failure. Also there are limitations if you are using the direct-path inserts.
Oracle vison for high availability is to use RAC where you wnat to be protected against failure within a site and use DataGuard to protect yourself against the site failure.
Other solutions (Replication,Streams) will require you to change your application to incorporate the failure detection and switching logic.
there are several whitepapers on this topic:
http://www.oracle.com/technology/deploy/availability/techlisting.html#DR
Mike