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Quick Question #14: Why do we have Virtual IP in Oracle RAC

Why do we have a Virtual IP (VIP) in Oracle RAC 10g or 11g? Why does it just return a dead connection when its primary node fails?

The goal is application availability with the shortest disruption time possible.

When a node fails, the VIP associated with it is automatically failed over to some other node. When this occurs, the following things happen. Vip resources in CRS (ora.node.vip)

(1) VIP detects public network failure which generates a FAN event.  ( A FAN event is an fast application notification event and ONS captures and publishes to the subscriber in RAC the subscriber can be listener)

(2) the new node re-arps (see arpa)  the world indicating a new MAC address for the IP.

(3) connected clients subscribing to FAN immediately receive ORA-3113 error or equivalent. Those not subscribing to FAN will eventually time out.

(4) New connection requests rapidly traverse the tnsnames.ora address list skipping over the dead nodes, instead of having to wait on TCP-IP timeouts (default 10 mins)

Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don't really have a good HA solution without using VIPs and FAN. The easiest way to use FAN is to use an integrated client with Fast Connection Failover (FCF) such as JDBC, OCI, or ODP.NET.

November 27th, 2012 | Tags: | Category: Quick Questions, RAC

1 comment to Quick Question #14: Why do we have Virtual IP in Oracle RAC