For DBA, if a database is up and running, everything seems beautiful..!! But once a state change happens in a database, we don’t know will it take 2 min to overcome it or it will eat our infinite time.

When we talk about Oracle RAC, we know there are multiple resources are available to give High Availability and Load balancing feature. And when we are having multiple resources available for multiple instances, multiple services and multiple listeners to serve us, a state change can cause a performance problem.

Let us take an example of a node failure.

When a node fails without closing sockets, all sessions that are blocked in an IO [read or write] wait for TCP keepalive. This wait status is the typical condition for an application using the database.

Sessions processing the last result are even worse off, not receiving an interrupt until the next data is requested.

Here we can take advantage of FAN [Fast Application Notification].

To read more about FAN Fast Application Notification [FAN] overview

  1. FAN eliminates application waiting on TCP timeouts as Oracle RAC notifies the cluster about FAN events the minutes any changes have occurred and we can handle those events.
  2. It eliminates time wasted processing the last result at the client after a failure has occurred.
  3. It eliminates time wasted executing work on slow, hung or dead nodes.

We can take advantage of server-side callouts FAN and do following things.

  1. Whenever FAN events occur we can log that so that helps us for administration in future.
  2. We can use paging or SMS DBA to open tickets when any resource fails to restart.
  3.  Change resource plans or to shut down services when the number of available instances decreases, thus preventing further load on the cluster and keeping the RAC running until another healthy node is added to the cluster.
  4.  We can automate the fail service back to the PREFERRED instances when required.

Stay tuned for More articles on Oracle RAC 

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