PolarDB:DBMS_AQ

You can use the ENQUEUE stored procedure to add an entry to a queue. Syntax:

ENQUEUE(
  queue_name IN VARCHAR2,
  enqueue_options IN DBMS_AQ.ENQUEUE_OPTIONS_T,
  message_properties IN DBMS_AQ.MESSAGE_PROPERTIES_T,
  payload IN <type_name>,
  msgid OUT RAW)

Parameters

• queue_name
  The name of an existing queue. This name may be a schema-qualified name.

  Note

  • If you omit the schema name, the server uses the schema that is specified by SEARCH_PATH.
  • To include special characters or use a case-sensitive name, enclose the name in double quotation marks.
• enqueue_options
  enqueue_options is a value of the enqueue_options_t type.

  DBMS_AQ.ENQUEUE_OPTIONS_T IS RECORD(
    visibility BINARY_INTEGER DEFAULT ON_COMMIT,
    relative_msgid RAW(16) DEFAULT NULL,
    sequence_deviation BINARY INTEGER DEFAULT NULL,
    transformation VARCHAR2(61) DEFAULT NULL,
    delivery_mode PLS_INTEGER NOT NULL DEFAULT PERSISTENT);

  The following table lists the only parameter values that are supported by enqueue_options_t.

  Parameter	Default value
  visibility	ON_COMMIT
  delivery_mode	PERSISTENT
  sequence_deviation	NULL
  transformation	NULL
  relative_msgid	NULL

• message_properties
  message_properties is a value of the message_properties_t type.

        message_properties_t IS RECORD(
      priority INTEGER,
      delay INTEGER,
      expiration INTEGER,
      correlation CHARACTER VARYING(128) COLLATE pg_catalog."C",
      attempts INTEGER,
      recipient_list"AQ$_RECIPIENT_LIST_T",
      exception_queue CHARACTER VARYING(61) COLLATE pg_catalog."C",
      enqueue_time TIMESTAMP WITHOUT TIME ZONE,
        state INTEGER,
       original_msgid BYTEA,
        transaction_group CHARACTER VARYING(30) COLLATE pg_catalog."C",
        delivery_mode INTEGER
      DBMS_AQ.PERSISTENT);

  The following table describes the values that are supported by message_properties_t.

  Parameter	Description
  priority	If the queue table definition includes sort_list that references priority, this parameter affects the order in which messages are dequeued. A lower value specifies a higher dequeuing priority.
  delay	The number of seconds elapsed before a message becomes available for dequeuing. Alternatively, you can set this parameter to NO_DELAY.
  expiration	The number of seconds elapsed before a message expires.
  correlation	The message associated with the entry. Default value: NULL.
  attempts	The number of attempts to dequeue the message. This value is maintained by the system.
  exception_queue	The name of an exception queue. If the message expires or is dequeued by a transaction that is rolled back for a number of times, the message is moved to this queue.
  enqueue_time	The time when the entry was added to the queue.
  state	This parameter is maintained by DBMS_AQ. Valid values: DBMS_AQ.READY: The queue entry is not delayed. DBMS_AQ.WAITING: The queue entry is ready for being processed. DBMS_AQ.PROCESSED: The queue entry has been processed. DBMS_AQ.EXPIRED: The queue entry has been moved to the exception queue.
  original_msgid	This parameter is used for compatibility and can be ignored.
  transaction_group	This parameter is used for compatibility and can be ignored.

• payload

  You can use the payload parameter to provide the data that is associated with the queue entry. The payload type must match the type that is specified when you create the corresponding queue table. For more information, see CREATE_QUEUE_TABLE.

• msgid

  You can use the msgid parameter to retrieve a unique message identifier that is generated by the system.

The following anonymous block calls DBMS_AQ.ENQUEUE to add a message to a queue that is named work_order:

DECLARE

  enqueue_options    DBMS_AQ.ENQUEUE_OPTIONS_T;
  message_properties DBMS_AQ.MESSAGE_PROPERTIES_T;
  message_handle     raw(16);
  payload            work_order;

BEGIN

  payload := work_order('Smith', 'system upgrade');

DBMS_AQ.ENQUEUE(
  queue_name         => 'work_order',
  enqueue_options    => enqueue_options,
  message_properties => message_properties,
  payload            => payload,
  msgid              => message_handle
    );
 END;

You can use the DEQUEUE stored procedure to dequeue a message. Syntax:

DEQUEUE(
  queue_name IN VARCHAR2,
  dequeue_options IN DBMS_AQ.DEQUEUE_OPTIONS_T,
  message_properties OUT DBMS_AQ.MESSAGE_PROPERTIES_T,
  payload OUT type_name,
  msgid OUT RAW)

Parameters

• queue_name
  The name of an existing queue. This name may be a schema-qualified name.

  Note

  • If you omit the schema name, the server uses the schema that is specified by SEARCH_PATH.
  • To include special characters or use a case-sensitive name, enclose the name in double quotation marks.
• dequeue_options
  dequeue _options is a value of the dequeue_options_t type.

  DEQUEUE_OPTIONS_T IS RECORD(
    consumer_name CHARACTER VARYING(30),
    dequeue_mode INTEGER,
    navigation INTEGER,
    visibility INTEGER,
    wait INTEGER,
    msgid BYTEA,
    correlation CHARACTER VARYING(128),
    deq_condition CHARACTER VARYING(4000),
    transformation CHARACTER VARYING(61),
    delivery_mode INTEGER);

  The following table describes the values that are supported by dequeue_options_t.

  Parameter	Description
  consumer_name	Must be NULL.
  dequeue_mode	The locking behavior of the dequeuing operation. Valid values: DBMS_AQ.BROWSE: reads a message without obtaining a lock. DBMS_AQ.LOCKED: reads a message after a lock is obtained. DBMS_AQ.REMOVE: reads a message before the message is deleted. DBMS_AQ.REMOVE_NODATA: reads a message but does not delete the message.
  navigation	Identifies the message to be retrieved. Valid values: FIRST_MESSAGE: the first message in the queue that matches the search keyword. NEXT_MESSAGE: the next available message that matches the first keyword.
  visibility	Must be ON_COMMIT: If you roll back the current transaction, the dequeued item remains in the queue.
  wait	Must be a number larger than 0, or one of the following values: DBMS_AQ.FOREVER: waits indefinitely. DBMS_AQ.NO_WAIT: does not wait.
  msgid	The ID of the message to be dequeued.
  correlation	This parameter is used for compatibility and can be ignored.
  deq_condition	A VARCHAR2 expression that calculates a BOOLEAN value and specifies whether a message must be dequeued.
  transformation	This parameter is used for compatibility and can be ignored.
  delivery_mode	Must be PERSISTENT. Buffered messages are not supported in this mode.

• message_properties
  message_properties is a value of type message_properties_t:

      message_properties_t IS RECORD(
      priority INTEGER,
      delay INTEGER,
      expiration INTEGER,
      correlation CHARACTER VARYING(128) COLLATE pg_catalog."C",
      attempts INTEGER,
      recipient_list"AQ$_RECIPIENT_LIST_T",
      exception_queue CHARACTER VARYING(61) COLLATE pg_catalog."C",
      enqueue_time TIMESTAMP WITHOUT TIME ZONE,
      state INTEGER,
      original_msgid BYTEA,
      transaction_group CHARACTER VARYING(30) COLLATE pg_catalog."C",
      delivery_mode INTEGER
    DBMS_AQ.PERSISTENT);

  The following table describes the values that are supported by message_properties_t.

  Parameter	Description
  priority	If the queue table definition includes sort_list that references priority, this parameter affects the order in which messages are dequeued. A lower value specifies a higher dequeuing priority.
  delay	The number of seconds elapsed before a message is available for dequeuing. The NO_DELAY constant specifies that a message is dequeued immediately after the message is available.
  expiration	The number of seconds elapsed before a message expires.
  correlation	The message associated with the entry. Default value: NULL.
  attempts	The number of attempts to dequeue the message. This value is maintained by the system.
  exception_queue	The name of an exception queue. If the message expires or is dequeued by a transaction that is rolled back for a number of times, the message is moved to this queue.
  enqueue_time	The time when the entry was added to the queue.
  state	This parameter is maintained by DBMS_AQ. Valid values: DBMS_AQ.WAITING: The queue entry is not delayed. DBMS_AQ.READY: The queue entry is ready for being processed. DBMS_AQ.PROCESSED: The queue entry has been processed. DBMS_AQ.EXPIRED: The queue entry has been moved to the exception queue.
  original_msgid	This parameter is used for compatibility and can be ignored.
  transaction_group	This parameter is used for compatibility and can be ignored.
  delivery_mode	This parameter is not supported. Specify a value of DBMS_AQ.PERSISTENT.

• payload

  You can use the payload parameter to retrieve the payload of a message that is involved in a dequeuing operation. The payload type must match the type that is specified when you create the queue table.

• msgid

  You can use the msgid parameter to retrieve a unique message identifier.

The following anonymous block calls DBMS_AQ.DEQUEUE to retrieve a message from the queue and payload:

DECLARE

  dequeue_options    DBMS_AQ.DEQUEUE_OPTIONS_T;
  message_properties DBMS_AQ.MESSAGE_PROPERTIES_T;
  message_handle     raw(16);
  payload            work_order;

BEGIN
  dequeue_options.dequeue_mode := DBMS_AQ.BROWSE;

  DBMS_AQ.DEQUEUE(
    queue_name         => 'work_queue',
    dequeue_options    => dequeue_options,
    message_properties => message_properties,
    payload            => payload,
    msgid              => message_handle
  );

  DBMS_OUTPUT.PUT_LINE(
  'The next work order is [' || payload.subject || '].'
  );
END;

The payload is displayed by DBMS_OUTPUT.PUT_LINE.

You can use the REGISTER stored procedure to register an email address, procedure, or URL that is used to receive notifications when an item is enqueued or dequeued. Syntax:

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

Parameters

• reg_list
  You can use the reg_list parameter to specify a list of the AQ$_REG_INFO_LIST type and provides the information about each subscription that you want to register. The type of each entry in the list is AQ$_REG_INFO. The following table describes the attributes that can be included in each entry.

  Attribute	Type	Description
  name	VARCHAR2 (128)	The name of a subscription. This name may be a schema-qualified name.
  namespace	NUMERIC	The value must be DBMS_AQ.NAMESPACE_AQ (0).
  callback	VARCHAR2 (4000)	Describes the action to be performed upon notification. Only PL/SQL stored procedures are supported. The procedures are called in the following form: plsql://schema.procedure. The following items describe the fields in this form: The schema field specifies the schema in which the stored procedure resides. The procedure field specifies the name of the stored procedure to be notified.
  context	RAW (16)	A user-defined value required by the stored procedure.

• count

  You can use the count parameter to specify the number of entries in reg_list.

The following anonymous block calls DBMS_AQ.REGISTER to register stored procedures that are notified when an item is added to or deleted from a queue. A set of attributes of the sys.aq$_reg_info type is provided for each subscription that is identified in the DECLARE section.

DECLARE
   subscription1 sys.aq$_reg_info;
   subscription2 sys.aq$_reg_info;
   subscription3 sys.aq$_reg_info;
   subscriptionlist sys.aq$_reg_info_list;
BEGIN
   subscription1 := sys.aq$_reg_info('q', DBMS_AQ.NAMESPACE_AQ, 'plsql://assign_worker?PR=0',HEXTORAW('FFFF'));
   subscription2 := sys.aq$_reg_info('q', DBMS_AQ.NAMESPACE_AQ, 'plsql://add_to_history?PR=1',HEXTORAW('FFFF'));
   subscription3 := sys.aq$_reg_info('q', DBMS_AQ.NAMESPACE_AQ, 'plsql://reserve_parts?PR=2',HEXTORAW('FFFF'));

   subscriptionlist := sys.aq$_reg_info_list(subscription1, subscription2, subscription3);
   dbms_aq.register(subscriptionlist, 3);
   commit;
  END;
   /

You can use the subscriptionlist parameter to specify a list of the sys.aq$_reg_info_list type and contains the sys.aq$_reg_info objects that were described. The list name and the object count are passed to dbms_aq.register.

You can use the UNREGISTER stored procedure to disable notifications that are related to enqueuing and dequeuing. Syntax:

UNREGISTER(
  reg_list IN SYS.AQ$_REG_INFO_LIST,
  count
IN NUMBER)

Parameters

• reg_list

  You can use the reg_list parameter to specify a list of the AQ$_REG_INFO_LIST type and provides the information about each subscription that you want to register. The type of each entry in the list is AQ$_REG_INFO. The following table describes the attributes that can be included in each entry.

  Attribute	Type	Description
  name	VARCHAR2 (128)	The name of a subscription. This name may be a schema-qualified name.
  namespace	NUMERIC	The value must be DBMS_AQ.NAMESPACE_AQ (0).
  callback	VARCHAR2 (4000)	Describes the action to be performed upon notification. Only PL/SQL stored procedures are supported. The procedures are called in the following form: plsql://schema.procedure. The following items describe the fields in this form: The schema field specifies the schema in which the stored procedure resides. The procedure field specifies the name of the stored procedure to be notified.
  context	RAW (16)	A user-defined value required by the stored procedure.

• count

  You can use the count parameter to specify the number of entries in reg_list.

You can use the subscriptionlist parameter to specify a list of the sys.aq$_reg_info_list type and contains the sys.aq$_reg_info objects that were described. The list name and object count are passed to dbms_aq.unregister.

DECLARE
   subscription1 sys.aq$_reg_info;
   subscription2 sys.aq$_reg_info;
   subscription3 sys.aq$_reg_info;
   subscriptionlist sys.aq$_reg_info_list;
BEGIN
   subscription1 := sys.aq$_reg_info('q', DBMS_AQ.NAMESPACE_AQ, 'plsql://assign_worker?PR=0',HEXTORAW('FFFF'));
   subscription2 := sys.aq$_reg_info('q', DBMS_AQ.NAMESPACE_AQ, 'plsql://add_to_history?PR=1',HEXTORAW('FFFF'));
   subscription3 := sys.aq$_reg_info('q', DBMS_AQ.NAMESPACE_AQ, 'plsql://reserve_parts?PR=2',HEXTORAW('FFFF'));

   subscriptionlist := sys.aq$_reg_info_list(subscription1, subscription2, subscription3);
   dbms_aq.unregister(subscriptionlist, 3);
   commit;
  END;
   /