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Oracle® Database PL/SQL Packages and Types Reference
11g Release 2 (11.2)

Part Number E16760-04
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22 DBMS_AQ

The DBMS_AQ package provides an interface to Oracle Streams Advanced Queuing (AQ).

See Also:

This chapter contains the following topics:


Using DBMS_AQ


Constants

The DBMS_AQ package uses the constants shown in Table 22-1.

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.

Note:

The sequence_deviation attribute has no effect in releases prior to Oracle Streams AQ 10g Release 1 (10.1) if message_grouping parameter of DBMS_AQADM subprograms is set to TRANSACTIONAL. The sequence deviation feature is deprecated in Oracle Streams AQ 10g Release 2 (10.2).

Table 22-1 Enumerated Constants

Parameter Options Type Description

VISIBILITY

IMMEDIATE

   

.

ON_COMMIT

   

DEQUEUE_MODE

BROWSE

   

.

LOCKED

   

.

REMOVE

   

.

REMOVE_NODATA

   

NAVIGATION

FIRST_MESSAGE

   

.

NEXT_MESSAGE

   

STATE

WAITING

   

.

READY

   

.

PROCESSED

   

.

EXPIRED

   

SEQUENCE_DEVIATION

BEFORE

   

.

TOP

   

WAIT

FOREVER

BINARY_INTEGER

 

.

NO_WAIT

BINARY_INTEGER

 

DELAY

NO_DELAY

   

EXPIRATION

NEVER

   

NAMESPACE

NAMESPACE_AQ

   

.

NAMESPACE_ANONYMOUS

   

NTFN_GROUPING_CLASS

NFTN_GROUPING_CLASS_TIME

NUMBER

 

NTFN_GROUPING_TYPE

NTFN_GROUPING_TYPE_SUMMARY

NUMBER

 

.

NTFN_GROUPING_TYPE_LAST

NUMBER

 

NTFN_GROUPING_REPEAT_COUNT

NTFN_GROUPING_FOREVER

NUMBER

 


Data Structures

Table 22-2 DBMS_AQ Data Structures

Data Structures Description

Object Name

Names database objects

Type Name

Defines queue types

Oracle Streams AQ PL/SQL Callback

Specifies the user-defined PL/SQL procedure, defined in the database to be invoked on message notification


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 Language 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

Table 22-3 Type Name Attributes

Attribute Description

object_type

Maximum number of attributes in the object type is limited to 900.

"RAW"

To store payload of type RAW, Oracle Streams AQ creates a queue table with a LOB column as the payload repository. The theoretical maximum size of the message payload is the maximum amount of data that can be stored in a LOB column. However, the maximum size of the payload is determined by which programmatic environment you use to access Oracle Streams AQ. For PL/SQL, Java and precompilers the limit is 32K; for the OCI the limit is 4G. Because the PL/SQL enqueue and dequeue interfaces accept RAW buffers as the payload parameters you will be limited to 32K bytes. In OCI, the maximum size of your RAW data will be limited to the maximum amount of contiguous memory (as an OCIRaw is simply an array of bytes) that the OCI Object Cache can allocate. Typically, this will be at least 32K bytes and much larger in many cases.

Because LOB columns are used for storing RAW payload, the Oracle Streams AQ administrator can choose the LOB tablespace and configure the LOB storage by constructing a LOB storage string in the storage_clause parameter during queue table creation time.


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

Table 22-4 Oracle Streams AQ PL/SQL Callback Attributes

Attribute Description

context

Specifies the context for the callback function that was passed by dbms_aq.register. See AQ$_REG_INFO Type.

reginfo

See AQ$_REG_INFO Type.

descr

See AQ$_DESCRIPTOR Type

payload

If a notification message is expected for a raw payload enqueue then this contains the raw payload that was enqueued into a non persistent queue. In case of a persistent queue with raw payload this parameter will be null.

payloadl

Specifies the length of payload. If payload is null, payload1 = 0.


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

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

Table 22-5 DBMS_AQ Package Subprograms

Subprograms Description

BIND_AGENT Procedure

Creates an entry for an Oracle Streams AQ agent in the LDAP directory

DEQUEUE Procedure

Dequeues a message from the specified queue

DEQUEUE_ARRAY Function

Dequeues an array of messages from the specified queue

ENQUEUE Procedure

Adds a message to the specified queue

ENQUEUE_ARRAY Function

Adds an array of messages to the specified queue

LISTEN Procedures

Listen to one or more queues on behalf of a list of agents

POST Procedure

Posts to a anonymous subscription which allows all clients who are registered for the subscription to get notifications

REGISTER Procedure

Registers for message notifications

UNBIND_AGENT Procedure

Removes an entry for an Oracle Streams AQ agent from the LDAP directory

UNREGISTER Procedure

Unregisters a subscription which turns off notification


Note:

DBMS_AQ does not have a purity level defined; therefore, you cannot call any procedure in this package from other procedures that have RNDS, WNDS, RNPS or WNPS constraints defined.

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

Table 22-6 BIND_AGENT Procedure Parameters

Parameter Description

agent

Agent that is to be registered in LDAP server.

certificate

Location (LDAP distinguished name) of the "organizationalperson" entry in LDAP whose digital certificate (attribute usercertificate) is to be used for this agent. Example: "cn=OE, cn=ACME, cn=com" is a distinguished name for a OrganizationalPerson OE whose certificate will be used with the specified agent.


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

Table 22-7 DEQUEUE Procedure Parameters

Parameter Description

queue_name

Specifies the name of the queue.

dequeue_options

See DEQUEUE_OPTIONS_T Type.

message_properties

See MESSAGE_PROPERTIES_T Type.

payload

Not interpreted by Oracle Streams AQ. The payload must be specified according to the specification in the associated queue table. For the definition of type_name refer to Type Name.

msgid

System generated identification of the message.


Usage Notes

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

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.

Note:

It may be more efficient to use the FIRST_MESSAGE navigation option when messages are concurrently enqueued. If the FIRST_MESSAGE option is not specified, Oracle Streams AQ continually generates the snapshot as of the first dequeue command, leading to poor performance. If the FIRST_MESSAGE option is specified, then Oracle Streams AQ uses a new snapshot for every dequeue command.

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:


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

Table 22-8 DEQUEUE_ARRAY Function Parameters

Parameter Description

queue_name

The queue name from which messages are dequeued (same as single-row dequeue).

dequeue_options

The set of options which will be applied to all messages in the array (same as single-row dequeue).

array_size

The number of elements to dequeue.

message_properties_array

A record containing an array corresponding to each message property. Each payload element has a corresponding set of message properties. See MESSAGE_PROPERTIES_ARRAY_T Type.

payload_array

An array of dequeued payload data. "<COLLECTION_1>" can be an associative array, varray or nested table in its PL/SQL representation.

msgid_array

An array of message IDs of the dequeued messages. See MSGID_ARRAY_T Type.

error_array

Currently not implemented


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:

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

Table 22-9 ENQUEUE Procedure Parameters

Parameter Description

queue_name

Specifies the name of the queue to which this message should be enqueued. The queue cannot be an exception queue.

enqueue_options

See ENQUEUE_OPTIONS_T Type.

message_properties

See MESSAGE_PROPERTIES_T Type.

payload

Not interpreted by Oracle Streams AQ. The payload must be specified according to the specification in the associated queue table. NULL is an acceptable parameter. For the definition of type_name refer to Type Name.

msgid

System generated identification of the message. This is a globally unique identifier that can be used to identify the message at dequeue time.


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.

Note:

The sequence_deviation attribute has no effect in releases prior to Oracle Streams AQ 10g Release 1 (10.1) if message_grouping parameter of DBMS_AQADM subprograms is set to TRANSACTIONAL. The sequence deviation feature is deprecated in Oracle Streams AQ 10g Release 2 (10.2).

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:


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

Table 22-10 ENQUEUE_ARRAY Function Parameters

Parameter Description

queue_name

The queue name in which messages are enqueued (same as single-row enqueue).

enqueue_options

See ENQUEUE_OPTIONS_T Type.

array_size

The number of elements to enqueue.

message_properties_array

A record containing an array corresponding to each message property. For each property, the user must allocate array_size elements. See MESSAGE_PROPERTIES_ARRAY_T Type.

payload_array

An array of payload data. "<COLLECTION_1>" can be an associative array, VARRAY, or nested table in its PL/SQL representation.

msgid_array

An array of message IDs for the enqueued messages. If an error occurs for a particular message, then its corresponding message ID is null. See MSGID_ARRAY_T Type.

error_array

Currently not implemented


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

Table 22-11 LISTEN Procedure Parameters

Parameter Description

agent_list

List of agents to listen for

wait

Time out for the listen call in seconds. By default, the call will block forever.

listen_delivery_mode

The caller specifies whether it is interested in persistent, buffered messages or both types of messages, specifying a delivery mode of DBMS_AQ.PERSISTENT or DBMS_AQ.BUFFERED or DBMS_AQ.PERSISTENT_OR_BUFFERED

agent

Agent with a message available for consumption

message_delivery_mode

Returns the message type along with the queue and consumer for which there is a message


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.

Note:

You cannot call LISTEN on nonpersistent queues.

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

Table 22-12 POST Procedure Parameters

Parameter Description

post_list

Specifies the list of anonymous subscriptions to which you want to post. It is a list of AQ$_POST_INFO_LIST Type.

post_count

Specifies the number of entries in the post_list.


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

Table 22-13 REGISTER Procedure Parameters

Parameter Description

reg_list

Specifies the list of subscriptions to which you want to register for message notifications. It is a list of AQ$_REG_INFO Type.

count

Specifies the number of entries in the reg_list.


Usage Notes

See Also:

Chapter 24, "DBMS_AQELM" for more information on e-mail and 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

Table 22-14 BIND_AGENT Procedure Parameters

Parameter Description

agent

Agent that is to be removed from the LDAP server



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

Table 22-15 UNREGISTER Procedure Parameters

Parameter Description

reg_list

Specifies the list of subscriptions to which you want to register for message notifications. It is a list of AQ$_REG_INFO Type.

reg_count

Specifies the number of entries in the reg_list.


Usage Notes

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