Wednesday, July 11, 2012

Listener.ora and Oraagent in RAC 11gR2

Topic: An investigation of a few details of the implementation of listeners in 11gR2, including the configuration of listener.ora in RAC and the role of the cluster process 'oraagent'.

11gR2 comes with several important changes and improvements to the clusterware in general and in particular the way listeners are managed. While the listener process is still the 'good old' process  tnslsnr (Linux and Unix), it is now started from the grid home (as opposed to database oracle home). Moreover listeners are divided in two classes: node listeners and scan listeners, although they use the same binary for both functions. There are many more details and instead of covering them here I'd rather reference this excellent review: Markus Michalewicz's presentation at TCOUG.

Oraagent takes good care of our listeners

  • Node listeners and scan listeners are configured at the clusterware level, for example with srvctl and the configuration is propagated to the listeners accordingly
    • this integration is more consistently enforced in 11gR2 than in previous versions
  • The oraagent process spawned by crsd takes care of our listeners in terms of configuration and monitoring
    • note that there is normally a second oraagent on the system which is spawned by ohasd and does not seem to come into play here
  • Notably in the listener.ora file we can see which configuration lines are being taken care of automatically by oraagent, as they are marked with the following comment: # line added by Agent
    • experiment on a test DB: delete one or more of the listener.ora configuration lines and restart the listener (for example with srvctl stop listener; srvctl start listener). The original configuration will reappear in listener.ora and the manually modified listener.ora will be renamed (with a timestamp suffix)
  • The agent creates and maintains the file: endpoints_listener.ora
    • this file is there for backward compatibility, see docs and/or support site for more info. 
    • experiment on test: delete the file and restart the listerner, oraagent will recreate the file.
  • Oraagent log can be found at: $GRID_HOME/log/{nodename}/agent/crsd/oraagent_oracle/oraagent_oracle.log
  • Oraagent monitors the functioning of each listener 
    • from the log file entries (see above about the location of the oraagent log file) we can see that each listener is monitored with a frequency of 60 seconds
  • Oraagent comes into action also at instance startup, when the instance is started with srvctl (as opposed to 'manually' started instance from sqlplus) and sets LOCAL_LISTENER parameter, dynamically (this is done with an alter system command and only if the parameter has not been set on spfile).

    Dynamic listening endpoints 

    • Where are the TCP/IP settings of my listeners in listener.ora? 
      • Only IPC endpoints are listed in listener.ora, this is at first puzzling, where are the TCP settings that in previous versions were listed in listener.ora? on!
    • Notes: 
      • endpoint=the address or connection point to the listener. The most known endpoint in the oracle DB world being TCP, port 1521
      • dynamic listening endpoint and dynamic service registration are both concepts related to listener activities, but they are distinct.
    • Oraagent connects to the listener via IPC and activates the TCP (TCPS, etc) endpoints as specified in the clusterware configuration
      • experiment on test: $GRID_HOME/bin/lsnrctl stop listener; $GRID_HOME/bin/lsnrctl start listener; Note that the latter command starts only the IPC endpoint. However oraagent is posted at listener startup and makes active the rest of the endpoints (notably listening on the TCP  port), this can be seen for example by running the following a few seconds after listener restart: $GRID_HOME/bin/lsnrctl status listener (which will list all the active endpoints)
    • Another way to say that is that the endpoints for the listener in RAC 11gR2 are configured in a  dynamic way: TCP (TCPS, etc) endpoints are activated at runtime by oraagent
      • this is indicated in the listener.ora by the new (undocumented) parameters ENABLE_GLOBAL_DYNAMIC_ENDPOINT_{LISTENER_NAME}=ON
    • Experiment on test on disabling dynamic listening endpoint:  
      • stop the listener: $GRID_HOME/bin/lsnrctl stop listener
      • edit listener.ora and set  ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER=OFF
      • start the listener: $GRID_HOME/bin/lsnrctl start listener
      • check listener.ora and check that the parameter edited above has not changed, that is  ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER=OFF 
      • in this case the TCP endpoint will not be started, that is the listener will be listening only on IPC. Check with: $GRID_HOME/bin/lsnrctl status listener 
      • note: if we try do the same exercise by stopping and starting the listener with srvctl, as it would be the typical way to do it, we will see that the parameter ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER in listener.ora will be set again to ON. This will activate again dynamic listening endpoints, which is something we want in production, but not for this exercise!
    • Note: the examples have been tested on RAC for Linux. ORACLE_HOME needs to be set to point to the grid home (and TNS_ADMIN if used at all, needs to be set to $GRID_HOME/network/admin)

    I don't need to edit listener.ora any more, or do I?

    • We have seen above that the most important configurations related to listener.ora are automated via oraagent and the clusterware in general
    • There are additional listener.ora parameters that are not managed by the clusterware in11gR2 and need to be configured in listener.ora in case we want to use them
    • The steps for the configuration are very well described in support note 1340831.1. Here we just mention that for a 2-node RAC the following parameters will be needed in listener.ora (note parameters taken from listener.ora on RAC for Linux):
    WALLET_LOCATION =  (SOURCE =(METHOD = FILE)(METHOD_DATA =(DIRECTORY = ..put here directory of wallet..)))


    The handling of listeners in 11gR2 RAC has become much more integrated with the clusterware and for most RAC configurations there is not much need to play with listener.ora any more. At a closer look of however, new parameters and overall some new rules of the game in the 11gR2 implementation are revealed, most notably the use of dynamic endpoint registration by the clusterware.


    1. Hello Luca,

      I think there are 2 typos in your interesting log entry
      1. The most none endpoint in the oracle DB world being TCP, port 1521 => the most KNOWN endpoint ...
      2. by not for this exercise! => BUT not for this exercise ...

      1. Thanks Pierre, I have now corrected the typos you found.

    2. If I have Oracle 11gR1 Database and Clients are using old Node-VIPS to connect, how will the Listener handle them, Can I have both Node-VIPS and Scan name specified on the remote_listener.