16 DBMS_AQ

Using DBMS_AQ

• Constants

• Data Structures

• Operational Notes

Constants

When using enumerated constants such as BROWSE, LOCKED, or REMOVE, the PL/SQL constants must be specified with the scope of the packages defining it. All types associated with the operational interfaces have to be prepended with DBMS_AQ. For example: DBMS_AQ.BROWSE. Table 16-1 lists the PL/SQL enumerated constants that require the prefix, DBMS_AQ.

Data Structures

Object Name

The object_name data structure names database objects. It applies to queues, queue tables, agent names, and object types.

Syntax

object_name := VARCHAR2;
object_name := [schema_name.]name;

Usage Notes

Names for objects are specified by an optional schema name and a name. If the schema name is not specified, the current schema is assumed. The name must follow object name guidelines in Oracle Database SQL Reference with regard to reserved characters. Schema names, agent names, and object type names can be up to 30 bytes long. Queue names and queue table names can be up to 24 bytes long.

Type Name

The type_name data structure defines queue types.

Syntax

type_name := VARCHAR2;
type_name := object_type | "RAW";

Attributes

Oracle Streams AQ PL/SQL Callback

The plsqlcallback data structure specifies the user-defined PL/SQL procedure, defined in the database to be invoked on message notification.

Syntax

If a notification message is expected for a RAW payload enqueue, then the PL/SQL callback must have the following signature:

procedure plsqlcallback(
  context  IN  RAW, 
  reginfo  IN  SYS.AQ$_REG_INFO, 
  descr    IN  SYS.AQ$_DESCRIPTOR, 
  payload  IN  RAW,
  payloadl IN  NUMBER);

Attributes

If the notification message is expected for an ADT payload enqueue, the PL/SQL callback must have the following signature:

procedure plsqlcallback(
  context  IN RAW, 
  reginfo  IN SYS.AQ$_REG_INFO, 
  descr    IN SYS.AQ$_DESCRIPTOR, 
  payload  IN VARCHAR2,
  payloadl IN NUMBER);

Operational Notes

• DBMS_AQ and DBMS_AQADM Java Classes

DBMS_AQ and DBMS_AQADM Java Classes

Java interfaces are available for DBMS_AQ and DBMS_AQADM. The Java interfaces are provided in the $ORACLE_HOME/rdbms/jlib/aqapi.jar. Users are required to have EXECUTE privileges on the DBMS_AQIN package to use these interfaces.

Summary of DBMS_AQ Subprograms

BIND_AGENT Procedure

This procedure creates an entry for an Oracle Streams AQ agent in the LDAP server.

Syntax

DBMS_AQ.BIND_AGENT(
   agent        IN SYS.AQ$_AGENT,
   certificate  IN VARCHAR2 default NULL);

Parameters

Usage Notes

In the LDAP server, digital certificates are stored as an attribute (usercertificate) of the OrganizationalPerson entity. The distinguished name for this OrganizationalPerson must be specified when binding the agent.

DEQUEUE Procedure

This procedure dequeues a message from the specified queue.

Syntax

DBMS_AQ.DEQUEUE (
   queue_name          IN      VARCHAR2,
   dequeue_options     IN      dequeue_options_t,
   message_properties  OUT     message_properties_t,
   payload             OUT     "<ADT_1>"
   msgid               OUT     RAW);

Parameters

Usage Notes

The search criteria for messages to be dequeued is determined by the following parameters in dequeue_options:

• consumer_name

• msgid

  Msgid uniquely identifies the message to be dequeued. Only messages in the READY state are dequeued unless msgid is specified.

• correlation

  Correlation identifiers are application-defined identifiers that are not interpreted by Oracle Streams AQ.

• deq_condition

  Dequeue condition is an expression based on the message properties, the message data properties and PL/SQL functions. A deq_condition is specified as a Boolean expression using syntax similar to the WHERE clause of a SQL query. This Boolean expression can include conditions on message properties, user data properties (object payloads only), and PL/SQL or SQL functions (as specified in the where clause of a SQL query). Message properties include priority, corrid and other columns in the queue table.

  To specify dequeue conditions on a message payload (object payload), use attributes of the object type in clauses. You must prefix each attribute with tab.user_data as a qualifier to indicate the specific column of the queue table that stores the payload.

  Example: tab.user_data.orderstatus='EXPRESS'

The dequeue order is determined by the values specified at the time the queue table is created unless overridden by the msgid and correlation ID in dequeue_options.

The database-consistent read mechanism is applicable for queue operations. For example, a BROWSE call may not see a message that is enqueued after the beginning of the browsing transaction.

The default NAVIGATION parameter during dequeue is NEXT_MESSAGE. This means that subsequent dequeues will retrieve the messages from the queue based on the snapshot obtained in the first dequeue. In particular, a message that is enqueued after the first dequeue command will be processed only after processing all the remaining messages in the queue. This is usually sufficient when all the messages have already been enqueued into the queue, or when the queue does not have a priority-based ordering. However, applications must use the FIRST_MESSAGE navigation option when the first message in the queue needs to be processed by every dequeue command. This usually becomes necessary when a higher priority message arrives in the queue while messages already-enqueued are being processed.

Messages enqueued in the same transaction into a queue that has been enabled for message grouping will form a group. If only one message is enqueued in the transaction, then this will effectively form a group of one message. There is no upper limit to the number of messages that can be grouped in a single transaction.

In queues that have not been enabled for message grouping, a dequeue in LOCKED or REMOVE mode locks only a single message. By contrast, a dequeue operation that seeks to dequeue a message that is part of a group will lock the entire group. This is useful when all the messages in a group need to be processed as an atomic unit.

When all the messages in a group have been dequeued, the dequeue returns an error indicating that all messages in the group have been processed. The application can then use the NEXT_TRANSACTION to start dequeuing messages from the next available group. In the event that no groups are available, the dequeue will time out after the specified WAIT period.

Using Secure Queues

For secure queues, you must specify consumer_name in the dequeue_options parameter. See DEQUEUE_OPTIONS_T Type for more information about consumer_name.

When you use secure queues, the following are required:

• You must have created a valid Oracle Streams AQ agent using DBMS_AQADM.CREATE_AQ_AGENT. See CREATE_AQ_AGENT Procedure .

• You must map the Oracle Streams AQ agent to a database user with dequeue privileges on the secure queue. Use DBMS_AQADM.ENABLE_DB_ACCESS to do this. See ENABLE_DB_ACCESS Procedure.

  See Also:

  Oracle Streams Concepts and Administration for information about secure queues

DEQUEUE_ARRAY Function

This function dequeues an array of messages and returns them in the form of an array of payloads, an array of message properties and an array of message IDs. This function returns the number of messages successfully dequeued.

Syntax

DBMS_AQ.DEQUEUE_ARRAY (
   queue_name                IN   VARCHAR2,
   dequeue_options           IN   dequeue_options_t,
   array_size                IN   pls_integer,
   message_properties_array  OUT  message_properties_array_t,
   payload_array             OUT  "<COLLECTION_1>",
   msgid_array               OUT  msgid_array_t,
   error_array               OUT  error_array_t)
RETURN pls_integer;

Parameters

Usage Notes

A nonzero wait time, as specified in dequeue_options, is recognized only when there are no messages in the queue. If the queue contains messages that are eligible for dequeue, then the DEQUEUE_ARRAY function will dequeue up to array_size messages and return immediately.

Dequeue by message_id is not supported. See DEQUEUE Procedure for more information on the navigation parameter. Existing NAVIGATION modes are supported. In addition, two new NAVIGATION modes are supported for queues enabled for message grouping:

• FIRST_MESSAGE_MULTI_GROUP

• NEXT_MESSAGE_MULTI_GROUP

  See Also:

  ENQUEUE_OPTIONS_T Type

For transaction grouped queues and ONE_GROUP navigation, messages are dequeued from a single transaction group only, subject to the array_size limit. In MULTI_GROUP navigation, messages are dequeued across multiple transaction groups, still subject to the array_size limit. ORA-25235 is returned to indicate the end of a transaction group.

DEQUEUE_ARRAY is not supported for buffered messages, but you can still use this procedure on individual buffered messages by setting array_size to one message.

ENQUEUE Procedure

This procedure adds a message to the specified queue.

Syntax

DBMS_AQ.ENQUEUE (
   queue_name          IN      VARCHAR2,
   enqueue_options     IN      enqueue_options_t,
   message_properties  IN      message_properties_t,
   payload             IN       "<ADT_1>",
   msgid               OUT     RAW);

Parameters

Usage Notes

The sequence_deviation parameter in enqueue_options can be used to change the order of processing between two messages. The identity of the other message, if any, is specified by the enqueue_options parameter relative_msgid. The relationship is identified by the sequence_deviation parameter.

Specifying sequence_deviation for a message introduces some restrictions for the delay and priority values that can be specified for this message. The delay of this message must be less than or equal to the delay of the message before which this message is to be enqueued. The priority of this message must be greater than or equal to the priority of the message before which this message is to be enqueued.

If a message is enqueued to a multiconsumer queue with no recipient, and if the queue has no subscribers (or rule-based subscribers that match this message), then Oracle error ORA_24033 is raised. This is a warning that the message will be discarded because there are no recipients or subscribers to whom it can be delivered.

Using Secure Queues

For secure queues, you must specify the sender_id in the messages_properties parameter. See MESSAGE_PROPERTIES_T Type for more information about sender_id.

When you use secure queues, the following are required:

• You must have created a valid Oracle Streams AQ agent using DBMS_AQADM.CREATE_AQ_AGENT. See CREATE_AQ_AGENT Procedure .

• You must map sender_id to a database user with enqueue privileges on the secure queue. Use DBMS_AQADM.ENABLE_DB_ACCESS to do this. See ENABLE_DB_ACCESS Procedure.

  See Also:

  Oracle Streams Concepts and Administration for information about secure queues

ENQUEUE_ARRAY Function

This function enqueues an array of payloads using a corresponding array of message properties. The output will be an array of message IDs of the enqueued messages.

Syntax

DBMS_AQ.ENQUEUE_ARRAY (
   queue_name                IN   VARCHAR2,
   enqueue_options           IN   enqueue_options_t,
   array_size                IN   pls_integer,
   message_properties_array  IN   message_properties_array_t,
   payload_array             IN   "<COLLECTION_1>",
   msgid_array               OUT  msgid_array_t,
   error_array               OUT  error_array_t)
RETURN pls_integer;

Parameters

Usage Notes

ENQUEUE_ARRAY is not supported for buffered messages, but you can still use this procedure on individual buffered messages by setting array_size to one message.

LISTEN Procedures

This procedure listens on one or more queues on behalf of a list of agents. The address field of the agent indicates the queue the agent wants to monitor. Only local queues are supported as addresses. Protocol is reserved for future use.

Syntax

DBMS_AQ.LISTEN (
   agent_list            IN    AQ$_AGENT_LIST_T,
   wait                  IN    BINARY_INTEGER DEFAULT DBMS_AQ.FOREVER, 
   agent                 OUT   SYS.AQ$_AGENT);

DBMS_AQ.LISTEN (
   agent_list             IN   AQ$_AGENT_LIST_T,
   wait                   IN   BINARY_INTEGER DEFAULT FOREVER, 
   listen_delivery_mode   IN   PLS_INTEGER DEFAULT DBMS_AQ.PERSISTENT,
   agent                  OUT  SYS.AQ$_AGENT,
   message_delivery_mode  OUT  PLS_INTEGER);

TYPE aq$_agent_list_t IS TABLE of aq$_agent INDEXED BY BINARY_INTEGER;
TYPE aq$_agent_list_t IS TABLE of aq$_agent INDEXED BY BINARY_INTEGER;

Parameters

Usage Notes

If agent-address is a multiconsumer queue, then agent-name is mandatory. For single-consumer queues, agent-name must not be specified.

This procedure takes a list of agents as an argument. You specify the queue to be monitored in the address field of each agent listed. You also must specify the name of the agent when monitoring multiconsumer queues. For single-consumer queues, an agent name must not be specified. Only local queues are supported as addresses. Protocol is reserved for future use.

This is a blocking call that returns when there is a message ready for consumption for an agent in the list. If there are messages for more than one agent, only the first agent listed is returned. If there are no messages found when the wait time expires, an error is raised.

A successful return from the LISTEN call is only an indication that there is a message for one of the listed agents in one the specified queues. The interested agent must still dequeue the relevant message.

POST Procedure

This procedure posts to a list of anonymous subscriptions that allows all clients who are registered for the subscriptions to get notifications.

Syntax

DBMS_AQ.POST (
  post_list       IN  SYS.AQ$_POST_INFO_LIST,
  post_count      IN  NUMBER);

Parameters

Usage Notes

This procedure is used to post to anonymous subscriptions which allows all clients who are registered for the subscriptions to get notifications. Several subscriptions can be posted to at one time.

REGISTER Procedure

This procedure registers an e-mail address, user-defined PL/SQL procedure, or HTTP URL for message notification.

Syntax

DBMS_AQ.REGISTER (
   reg_list     IN  SYS.AQ$_REG_INFO_LIST,
   count        IN  NUMBER);

Parameters

Usage Notes

This procedure is used to register for notifications. You can specify an e-mail address to which message notifications are sent, register a procedure to be invoked on a notification, or register an HTTP URL to which the notification is posted. Interest in several subscriptions can be registered at one time.

If you register for e-mail notifications, you should set the host name and port name for the SMTP server that will be used by the database to send e-mail notifications. If required, you should set the send-from e-mail address, which is set by the database as the sent from field. You need a Java-enabled database to use this feature.

If you register for HTTP notifications, you may want to set the host name and port number for the proxy server and a list of no-proxy domains that will be used by the database to post HTTP notifications.

UNBIND_AGENT Procedure

This procedure removes the entry for an Oracle Streams AQ agent from the LDAP server.

Syntax

DBMS_AQ.UNBIND_AGENT(
   agent    IN SYS.AQ$_AGENT);

Parameters

UNREGISTER Procedure

This procedure unregisters a subscription which turns off notifications.

Syntax

DBMS_AQ.UNREGISTER (
   reg_list     IN  SYS.AQ$_REG_INFO_LIST,
   reg_count    IN  NUMBER);

Parameters

Usage Notes

This procedure is used to unregister a subscription which turns off notifications. Several subscriptions can be unregistered from at one time.