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Tuesday, January 11, 2011

Service XDB is down alert in Grid Control

GridControl is reporting the XDB service as being down for RAC database.
In this thread it is investigated why this alert is thrown. We are using a RAC database called RACTST to show all settings and SQL queries.
It must be said that we haven't seen this alert being thrown for single-server databases. The Metric isn't even available in Grid Control there.

When creating a database with 'dbca' one can choose whether to use shared server setup. Even when shared server is disabled during database creation, afterwards the parameter 'dispatchers' is still set.
For anyone who is unfamiliar with the shared server term, consult the Oracle Database Administrators Guide at:

What do we see:
The default value for the dispatchers parameter looks like:

In this parameter the service 'RACTSTXDB' is configured. This service then is automatically made available. The service availability can be checked by querying the gv$services table:

SQL> select inst_id,name from gv$services where name='RACTSTXDB';
---------- ----------------------------------------------------------------

Because this is a 2-node RAC it is clearly shown that the service is available on both nodes.

When does the alert occur ?
Most DBA's disable the 'dispatchers' parameter whenever they choose to not use shared servers. Disabling the dispatcher is easily done by resetting the parameter from the spfile:

SQL> alter system reset dispatchers scope=spfile sid='*';

System altered.

It is also possible to turn of the dispatchers dynamically afterwards, by per using:

SQL> alter system reset dispatchers scope=memory sid='';

One can also restart the instance(s) to turn of the parameter after the spfile change.

Now wait for approx. 5 minutes, and voila, there is the alert:

Clicking on the alert shows a bit more detail, about when the alert occured:

A check in gv$services confirms the service being 'down' ( in fact it is gone):

SQL> select inst_id,name from gv$services where name='RACTSTXDB';

no rows selected.

The service is however still available in the database. A select from dba_services, still shows is as being known:

SQL> select name from dba_services where name='RACTSTXDB';
1 row selected.

Disabling the alert in GridControl would be a permanent "solution".
But that's more like a non-DBA workaround. You wouldn't be warned about any other real service being down.

There are three solutions to get rid of the alert:
- Either re-enable the dispatcher, or
- Remove the service from the database, or
- Learn to live with the alert being there.

The first is easy. Put back the 'dispatchers' parameter in the spfile with 'scope=both', and you're done. But stubborn as we are, DBA's never give up.

Well the second step, as said in the 'Problem' section, the alert is only thrown for RAC databases. For single instances, the Metric isn't even available in Grid Control.
In the RAC-FAQ on Oracle Support it says:

When I look at ALL_SERVICES view in my database I see services I did not create, what are they for?
You will always see a default database service that is the same name as your database. This service is available on all instances in the cluster. You will also see two services used by the database SYS$BACKGROUND (for background processes) and SYS$USERS (users who connect via BEQ or without using a service_name). You may also see services that end with XDB which are created for the XML DB feature and you will not be able to manage these services.

The meaning of the last phrase is that this service is not manageable with srvctl. It is unknown as a cluster resource. Is also says that belongs to the XML DB feature, so before proceeding with this thread consult MOS Note 416312.1 and the Oracle Forums thread:

If you're sure you're not using XML-Db features, then you are OK to drop the XDB service.
Use the following command to do so:

SQL> exec dbms_service.delete_service('RACTSTXDB');

PL/SQL procedure successfully completed.

This will drop the service. When done the alert in Grid Control will subsequently be cleared.
And ofcourse as a real DBA we first test this on our TEST systems, don't we ??

The last option 'Learn to live with it' is valid for those users that do use the XML-Db feature and are not able to drop the service. For them I would almost recommend to follow solution 1. It is easier to cope with a running but unused dispatcher, then with an Grid Control alert that sits in your face every day.

I nowhere found a reason why we should not be able to drop this service if we are not using XML-Db features. Therefore the real impact is not completely known. If anyone can elaborate about this subject, you're most welcome to do so.
And eh... if you mess up your production system by following the actions in this thread, start blaming yourself, not me. All above is done on a TEST server.


  1. thanks lot...quick and DBA commands

  2. Or just restart the service exec DBMS_SERVICE.START_SERVICE('service name');

  3. @Dennis Anderson:

    Thanks for the remark. Ofcourse I could have started the service, and it does indeed clear the alert. The focus however here lies in the fact that it is a default created service, which I - and a lot of other DBA's - don't use. I like to have things organized, to know which service is available for what purpose. I'm one of these guys who like to say: "If you don't use it, get rid of it!"
    That is the main reason for this thread.
    Thanks again.