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We are searching for some replacement of our mysql cluster - Oracle or pgsql. I read the whole document about HA in Oracle 11 database system, but I really was not able to understand it quite enough. What I did understand is that it is RAC which is doing HA. Is there any proxy behind like mysql-proxy ? Or the cluster is changing the IP address with some heart-beat like software? or applications must have in the connection string another destination in case of failure of the primary one? I need this so I would assess how much effort is needed for recoding core applications.

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closed as not constructive by Michael Hampton, Magellan, Brent Pabst, Scott Pack, Iain Oct 18 '12 at 18:17

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Please hire a professional that really understands infrastructural requirements and implications of a RAC setup. RAC consists of many components and isn't as simple as IP address changing over or anything of that sort. –  pfo Oct 17 '12 at 7:50
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2 Answers

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How the Oracle RAC works is a bit complicated, but dumbed down it is the following:

The Oracle RAC consists of Oracle database nodes. Each node has a local listener, and the whole cluster has one or more SCAN (Single Client Access Name) listeners. Each listener has its own virtual IP address. If a host dies, the listener address of the dead host is taken by an other host. The hosts should have a dedicated interconnect interface on which the heartbeat flows and the synchronization between the servers is done.

A client needs to connect to a SCAN listener only, and the IP address of that is constant (if the cluster has more SCANs, then the DNS should resolve a name to these addresses, making the clients connect to the SCANs using round-robin). When a client connects, the cluster redirects the client to the best local listener, but for this, the client does not need any further setup.

Oracle has fairly good documentation about RACs, but implementing and administering one is not straightforward (to say the least). You should heed pfo's advice and hire a professional if you want to use RAC.

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Thank you for this. I was exactly searching for this. –  John Oct 24 '12 at 7:33
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RAC is RAC / it isa black box prettz much. All HA stuff is handled on the RAC and driver levels. Application Recoding is only necessary as Oracle is not MySql.

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