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Oracle® Database Workspace Manager Developer's Guide
11g Release 2 (11.2)

Part Number E11826-02
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2 Workspace Manager Events

Certain applications may be interested in knowing what Workspace Manager operations are being performed and may want to take some actions based on that. Several types of Workspace Manager operations can be captured as events. Workspace Manager provides a framework for communicating these events asynchronously to the interested applications. The applications can then take some actions based on the event. Some scenarios in which events can be used include the following:

The Workspace Manager event framework is built on the Oracle Advanced Queuing (AQ) capability. Messaging features provided by AQ, such as asynchronous notification, persistence, propagation, access control, history, and rule-based subscription, can be used for Workspace Manager events.

Workspace Manager creates a multiconsumer queue where events are enqueued. The relevant information about the event, such as the type of event, the user and workspace that triggered the event, and the name of the versioned table, is initialized in the event payload and enqueued. Applications can subscribe to these events, optionally specifying a rule for their subscriptions. Only the events that satisfy the rule will be applicable to the subscriber. Subscribers can get event notification in variety of ways, such as listening for the events in the queue, registering a callback for notification, or explicitly dequeuing events from the queue.

Because events are communicated asynchronously to the other applications, the performance of the workspace operation generating the event is not affected.

Note:

To use Workspace Manager events in an application, you must understand the relevant AQ concepts and techniques described in Oracle Streams Advanced Queuing User's Guide.

This chapter contains the following major sections:

2.1 List of Workspace Manager Events

Table 2-1 lists the Workspace Manager events and when each occurs.

Table 2-1 Workspace Manager Events

Event Occurs

TABLE_MERGE_W_REMOVE_DATA

When MergeTable is invoked with remove_data set to TRUE.

TABLE_MERGE_WO_REMOVE_DATA

When MergeTable is invoked with remove_data set to FALSE.

TABLE_REFRESH

When RefreshTable is invoked.

TABLE_ROLLBACK

When RollbackTable is invoked.

WORKSPACE_COMPRESS

When CompressWorkspace or CompressWorkspaceTree is invoked.

WORKSPACE_CREATE

When CreateWorkspace is invoked.

WORKSPACE_MERGE_W_REMOVE

When MergeWorkspace is invoked with remove_workspace set to TRUE.

WORKSPACE_MERGE_WO_REMOVE

When MergeWorkspace is invoked with remove_workspace set to FALSE.

WORKSPACE_REFRESH

When RefreshWorkspace is invoked.

WORKSPACE_REMOVE

When RemoveWorkspace or RemoveWorkspaceTree is invoked.

WORKSPACE_ROLLBACK

When RollbackWorkspace is invoked.

WORKSPACE_VERSION

When a new version is created in the workspace as a result of the creation of an explicit or implicit savepoint. (Savepoints are described in Section 1.1.2.)


2.2 Event Parameters

When an event occurs, information is stored in parameters that are bundled into an object type called WMSYS.WM$EVENT_TYPE and enqueued into the event queue. A subscriber can dequeue the event object on receiving notification. Table 2-2 describes the Workspace Manager event parameters.

Table 2-2 Workspace Manager Event Parameters

Event Parameter Data Type Description

event_name

VARCHAR2(100)

Name indicating the type of event.

workspace_name

VARCHAR2(30)

Workspace that caused the event to occur.

parent_workspace_name

VARCHAR2(30)

Parent workspace of the workspace that caused the event to occur.

user_name

VARCHAR2(30)

User that caused the event to occur.

table_name

VARCHAR2(60)

Version-enabled table on which the event occurred. If this parameter does not apply to an event, it is null.

aux_params

WMSYS.WM$NV_PAIR_NT_TYPE (which is table of WMSYS.WM$NV_PAIR_TYPE)

A nested table of (name,value) pairs that can contain additional information about the event.

For TABLE_xxx events, it has one row containing the WHERE clause string used for the operation.

For WORKSPACE_VERSION events, it has one row containing the savepoint name associated with the newly created version.


2.3 ALLOW_CAPTURE_EVENTS System Parameter

Before you can capture any Workspace Manager events, you must use the SetSystemParameter procedure to set the Workspace Manager system parameter ALLOW_CAPTURE_EVENTS to the value ON. This does not, however, cause any events to be captured; to capture events, you must use the SetCaptureEvent procedure.

You can later disallow the capture of Workspace Manager events by using the SetSystemParameter procedure to set ALLOW_CAPTURE_EVENTS to the value OFF, but you must first ensure that no events are currently being captured. Example 2-1 shows the sequence of procedure calls for enabling and disabling the capture of all events, and starting and stopping the capture all events.

Example 2-1 Capturing Workspace Manager Events

-- Allow Workspace Manager events to be captured. (Required for SetCaptureEvent)
EXECUTE DBMS_WM.SetSystemParameter ('ALLOW_CAPTURE_EVENTS', 'ON');
-- Start capturing all Workspace Manager events.
EXECUTE DBMS_WM.SetCaptureEvent ('ALL_EVENTS','ON');
   .
   .
   .
-- Stop capturing all Workspace Manager events.
EXECUTE DBMS_WM.SetCaptureEvent ('ALL_EVENTS','OFF');
-- Disallow capture of Workspace Manager events.
EXECUTE DBMS_WM.SetSystemParameter ('ALLOW_CAPTURE_EVENTS', 'OFF');

2.4 AQ Operations and Workspace Manager Events

This section describes Advanced Queuing objects and techniques relevant to developers of applications that work with captured Workspace Manager events.

2.4.1 Workspace Manager Event Queue Administration

Workspace Manager creates a multiconsumer queue named WMSYS.WM$EVENT_QUEUE based on a queue table named WMSYS.WM$EVENT_QUEUE_TABLE. The queue payload type is WMSYS.WM$EVENT_TYPE, which is an object type.

AQ creates some views for the queue that can be used for administrative purposes. Table 2-3 describes the views of interest to developers of Workspace Manager applications.

Table 2-3 AQ Administrative Views for Workspace Manager

View Name Description

WMSYS.AQ$WM$EVENT_QUEUE_TABLE

Describes the queue table in which events are stored. This view can be used for querying the events. The roles AQ_ADMINISTRATOR_ROLE and WM_ADMIN_ROLE are granted select privileges on this view.

WMSYS.AQ$WM$EVENT_QUEUE_TABLE_S

Displays all the subscribers for the event queue; also displays the transformation for the subscriber if it was created with one. The roles AQ_ADMINISTRATOR_ROLE and WM_ADMIN_ROLE are granted select privileges on this view.

WMSYS.AQ$WM$EVENT_QUEUE_TABLE_R

Displays only the rule-based subscribers for all queues in a given queue table, as well as the text of the rule defined by each subscriber. Also displays the transformation for the subscriber if one was specified. The roles AQ_ADMINISTRATOR_ROLE and WM_ADMIN_ROLE are granted select privileges on this view.


2.4.2 Privileges and Access Control for Queues

The database administrator has several options for granting privileges and access to queues. Some possible scenarios include:

  • Grant the system privileges ENQUEUE ANY QUEUE and DEQUEUE ANY QUEUE directly to a database user by using the DBMS_AQADM.GRANT_SYSTEM_PRIVILEGE procedure, and optionally later revoke privileges by using the DBMS_AQADM.REVOKE_SYSTEM_PRIVILEGE procedure.

  • Grant the queue privileges ENQUEUE and DEQUEUE to the event queue WMSYS.WM$EVENT_QUEUE to a database user by using the DBMS_AQADM.GRANT_QUEUE_PRIVILEGE procedure, and optionally later revoke privileges by using the DBMS_AQADM.REVOKE_QUEUE_PRIVILEGE procedure.

  • Grant the role AQ_ADMINISTRATOR_ROLE to a database user to give that user administrative privileges on any queue.

Example 2-2 shows privileges being granted for a user to subscribe to the event queue and dequeue events.

Example 2-2 Granting Privileges for Queue Access

-- Do the following while connected as SYSDBA.
-- These privileges are required for the user to execute AQ packages.
grant execute on DBMS_AQ to SCOTT ;
grant execute on DBMS_AQADM to SCOTT ;

-- Grant privilege to SCOTT for subscribing to the event queue.
exec DBMS_AQADM.GRANT_SYSTEM_PRIVILEGE('MANAGE_ANY','SCOTT') ;

-- Grant privilege to SCOTT to dequeue events. (As an alternative, you could use
-- DBMS_AQADM.GRANT_QUEUE_PRIVILEGE to grant the DEQUEUE privilege on
-- WMSYS.WM$EVENT_QUEUE.)
exec DBMS_AQADM.GRANT_SYSTEM_PRIVILEGE('DEQUEUE_ANY','SCOTT') ;

2.4.3 Rule-Based Subscription

An event can be delivered to multiple recipients based on event parameters. You can define a rule-based subscription for the event queue as the mechanism for specifying interest in receiving events. Subscriber rules are then used to evaluate recipients for event delivery. A null rule indicates that the subscriber wishes to receive all events.

Example 2-3 creates a rule-based subscription for user SCOTT to deliver WORKSPACE_MERGE_WO_REMOVE events when the parent workspace is the LIVE workspace.

Example 2-3 Rule-Based Subscription for Workspace Manager Events

rem =================================================
rem Create queue subscribers
rem Register for MergeWorkspace event when
rem a workspace is merged to LIVE
rem =================================================

connect scott
-- Enter password when prompted.

DECLARE
    subscriber sys.aq$_agent;
BEGIN
    subscriber := sys.aq$_agent('MERGE_LISTENER', NULL, NULL);
    dbms_aqadm.add_subscriber(
      queue_name => 'WMSYS.WM$EVENT_QUEUE',
      subscriber => subscriber,
      rule => 'tab.user_data.event_name = ''WORKSPACE_MERGE_WO_REMOVE''
               and tab.user_data.parent_workspace_name = ''LIVE''');
END;
/

2.4.4 Listening for Events

The listen call is a blocking call that can be used to wait for events on a queue or a list of subscriptions. If the listen returns successfully, a dequeue must be used to retrieve the event.

Example 2-4 listens for events on an event queue.

Example 2-4 Listening for a Workspace Manager Event

rem ==============================================================
rem The following example shows how an application can listen for
rem an event. Explicit dequeue must be performed to get the actual
rem event parameters. The user SCOTT must have sufficient privileges 
rem as described in the "Access Control" section.
rem ==============================================================

connect scott
-- Enter password when prompted.

set serveroutput on

DECLARE
 qlist dbms_aq.aq$_agent_list_t;
 agent_w_msg sys.aq$_agent;
 listen_timeout exception;
 pragma exception_init(listen_timeout, -25254);
BEGIN
 qlist(0) := sys.aq$_agent('MERGE_LISTENER', 'WMSYS.WM$EVENT_QUEUE', NULL);

 dbms_output.put_line ('Listening on event queue.');

 BEGIN

 DBMS_AQ.LISTEN(
         agent_list => qlist,
         wait => 30,
         agent =>  agent_w_msg);

         dbms_output.put_line(agent_w_msg.name) ;

         /* The event can be dequeued here to get the event data */

 EXCEPTION
        when listen_timeout THEN
                null;
 END;

END;
/

2.4.5 Asynchronous Notification

Asynchronous notification allows clients to receive notification of an event of interest. The client can use it to monitor multiple subscriptions. The client does not have to be connected to the database to receive notifications regarding its subscriptions.

If an application registers for asynchronous notification of Workspace Manager events using callbacks, the minimum values for the following init.ora parameters should be:

  • aq_tm_processes = 1

  • job_queue_processes = 2

Example 2-5 registers for a callback to receive asynchronous notification of events.

Example 2-5 Receiving Asynchronous Notification of Events

rem =====================================================
rem Example of how to register for a callback to the event
rem queue on behalf of a subscriber. Subscriber has already
rem been defined in previous section. The callback is
rem invoked by the AQ framework whenever an event satisfying the
rem rule for the subscriber occurs. The minimum values for
rem the following init.ora parameters should be set as follows.
rem   aq_tm_processes = 1
rem   job_queue_processes = 2
rem The user SCOTT must have sufficient privileges.
rem ===========================================================

CONNECT scott
-- Enter password when prompted.

CREATE TABLE merge_log
(
  event_name      varchar2(30),
  workspace_name  varchar2(30),
  parent_workspace_name varchar2(30),
  user_name       varchar2(30)
);

CREATE OR REPLACE PROCEDURE scott.event_callback(
   context RAW , reginfo sys.aq$_reg_info, descr sys.aq$_descriptor, 
   payload VARCHAR2,  payloadl NUMBER)
AS
    deq_msgid           RAW(16);
    dopt                dbms_aq.dequeue_options_t;
    mprop               dbms_aq.message_properties_t;
    event               WMSYS.WM$EVENT_TYPE;
    no_messages         exception;
    pragma exception_init(no_messages, -25228);

BEGIN
    dopt.consumer_name := 'MERGE_LISTENER';
    dopt.wait := 30;
    dopt.msgid := descr.msg_id;

    dbms_aq.dequeue(
        queue_name => 'WMSYS.WM$EVENT_QUEUE',
        dequeue_options => dopt,
        message_properties => mprop,
        payload => event,
        msgid => deq_msgid);

    INSERT INTO merge_log VALUES (event.event_name, event.workspace_name,
      event.parent_workspace_name, event.user_name);

    /* Note: If there are additional parameters stored in
       "aux_params" attribute, it can be accessed using 
       event.aux_params(1).name, event.aux_params(1).value, 
       event.aux_params(2).name … and so on. The number of 
       parameters can be accessed using event.aux_params.count 
       when aux_params is not null.
     */
END;
/

grant execute on scott.event_callback to public ;

rem ==================================================
rem Register a callback for the event
rem Queue name and subscriber name have to be specified
rem while registering for a callback
rem ==================================================

DECLARE
  reginfo1            sys.aq$_reg_info;
  reginfolist         sys.aq$_reg_info_list;
BEGIN
  reginfo1 := sys.aq$_reg_info('WMSYS.WM$EVENT_QUEUE:MERGE_LISTENER',1,'plsql://scott.event_callback?PR=1',HEXTORAW('FF'));

  reginfolist := sys.aq$_reg_info_list(reginfo1);

  sys.dbms_aq.register(reginfolist, 1);

  COMMIT;

END;
/