2 Replies Latest reply on Dec 11, 2012 3:22 PM by 949766

    APEX Application behaviour in a RAC setup


      Caveat first: I'm pretty new to Oracle RAC and just looking into it as an option. We have an APEX application currently running in Oracle 11gR2 single node currently and are considering HA for this.

      My question is: What would be the expected behaviour seen by a User of an APEX application, in the event of a node failure, when running with an OHS / RAC configuration? Will they get "transparent fail-over" and see nothing or will they see an error?

      I appreciate I could post in the APEX forum, but feel that is probably more of a development forum and possibly someone here has had to look at things at this level.

      I have read what I think may be the definitive reference for this:
      but while it covers most of what I want I don't believe I have found an answer to my question

      This states:
      "The Transparent Application Failover (TAF) feature of Oracle Net Services is a runtime failover for high-availability environments. It enables client applications to automatically reconnect to the database if the connection fails and, optionally, resume a SELECT statement that was in progress. The reconnection happens automatically from within the Oracle Call Interface (OCI) library. For applications that do insert, update or delete transactions, the application must trap the error when the failure occurs, rollback the transaction, and then resubmit. If the application is not written to be TAF aware, the session will get disconnected."

      However (as I understand it) APEX runs in the database and would fail with the database, it isn't a typical "client application" connecting to Oracle via a TAF aware connection pool - it is essentially a large pl/sql package and TAF only covers SELECT statements not packages.

      May be I'm over-reading this and it's simpler than that: APEX/Mod_plsql might just handle it?
      - APEX User/HTTP session state is stored in database APEX: Understanding session state which is available on other nodes
      - Mod_plsql in OHS can detect the error returning and reissues the request to good server and APEX on that instance can retrieve Users/HTTP state and process the request (APEX/RAC doc states mod_plsql can see an error from database and cleanup connection up and form a new connection, but not that it will retry the request for the client into other APEX/DB node).

      I'm really just after a (transparent/non-transparent) statement based on experience, but an outline of how the components behave would be useful.

      Thanks in advance