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Oracle® Streams Advanced Queuing User's Guide
11g Release 1 (11.1)

B28420-02
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2 Basic Components

This chapter describes the Oracle Streams Advanced Queuing (AQ) basic components.

This chapter contains the following topics:

2.1 Object Name

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

This component names database objects. This naming convention applies to queues, queue tables, and object types.

Names for objects are specified by an optional schema name and a name. If the schema name is not specified, then the current schema is assumed. The name must follow the reserved character guidelines in Oracle Database SQL Language Reference. The schema name, agent name, and the object type name can each be up to 30 bytes long. However, queue names and queue table names can be a maximum of 24 bytes.

2.2 Type Name

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

This component defines queue types. For details on creating object types refer to Oracle Database Concepts. The maximum number of attributes in the object type is limited to 900.

To store payloads of type RAW, Oracle Streams AQ creates a queue table with a LOB column as the payload repository. The size of the payload is limited to 32K bytes of data. 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.


Note:

Payloads containing LOBs require users to grant explicit Select, Insert and Update privileges on the queue table for doing enqueues and dequeues.

2.3 AQ Agent Type

TYPE AQ$_AGENT IS OBJECT (
   name            VARCHAR2(30), 
   address         VARCHAR2(1024),
   protocol        NUMBER);

This component identifies a producer or a consumer of a message.

All consumers that are added as subscribers to a multiconsumer queue must have unique values for the AQ$_AGENT parameters. Two subscribers cannot have the same values for the NAME, ADDRESS, and PROTOCOL attributes for the AQ$_AGENT type. At least one of the three attributes must be different for two subscribers.

You can add subscribers by repeatedly using the DBMS_AQADM.ADD_SUBSCRIBER procedure up to a maximum of 1024 subscribers for a multiconsumer queue.

This type has three attributes:

2.4 AQ Recipient List Type

TYPE AQ$_RECIPIENT_LIST_T IS TABLE OF aq$_agent
           INDEX BY BINARY_INTEGER;
 

This component identifies the list of agents that receive a message.

2.5 AQ Agent List Type

TYPE AQ$_AGENT_LIST_T IS TABLE OF aq$_agent 
           INDEX BY BINARY INTEGER; 

This component identifies the list of agents for DBMS_AQ.LISTEN to listen for.

2.6 AQ Subscriber List Type

TYPE AQ$_SUBSCRIBER_LIST_T IS TABLE OF aq$_agent
          INDEX BY BINARY INTEGER;

This component identifies the list of subscribers that subscribe to this queue.

2.7 AQ Registration Information List Type

TYPE AQ$_REG_INFO_LIST AS VARRAY(1024) OF sys.aq$_reg_info;

This component identifies the list of registrations to a queue.

2.8 AQ Post Information List Type

TYPE AQ$_POST_INFO_LIST AS VARRAY(1024) OF sys.aq$_post_info;

This component identifies the list of anonymous subscriptions to which messages are posted.

2.9 AQ Registration Information Type

TYPE SYS.AQ$_REG_INFO IS OBJECT (
   name                              VARCHAR2(128),
   namespace                         NUMBER,
   callback                          VARCHAR2(4000),
   context                           RAW(2000)  DEFAULT NULL,
   qosflags                          NUMBER,
   timeout                           NUMBER
   ntfn_grouping_class               NUMBER,
   ntfn_grouping_value               NUMBER    DEFAULT 600,
   ntfn_grouping_type                NUMBER,
   ntfn_grouping_start_time          TIMESTAMP WITH TIME ZONE,
   ntfn_grouping_repeat_count   NUMBER);

This component identifies a producer or a consumer of a message. Its attributes are described in the following list. Attributes qosflags and timeout are part of Oracle Streams AQ 10g Release 2 (10.2) notification enhancements.

Table 2-1 AQ$_REG_INFO Type Attributes

Attribute Description
name Specifies the name of the subscription. The subscription name is of the form schema.queue if the registration is for a single consumer queue or schema.queue:consumer_name if the registration is for a multiconsumer queues.
namespace Specifies the namespace of the subscription. To receive notification from Oracle Streams AQ queues, the namespace must be DBMS_AQ.NAMESPACE_AQ. To receive notifications from other applications through DBMS_AQ.POST or OCISubscriptionPost(), the namespace must be DBMS_AQ.NAMESPACE_ANONYMOUS.
callback Specifies the action to be performed on message notification. For HTTP notifications, use http://www.company.com:8080. For e-mail notifications, use mailto://xyz@company.com. For raw message payload for the PLSQLCALLBACK procedure, use plsql://schema.procedure?PR=0. For user-defined type message payload converted to XML for the PLSQLCALLBACK procedure, use plsql://schema.procedure?PR=1
context Specifies the context that is to be passed to the callback function
qosflags Can be set to one or more of the following values to specify the notification quality of service:
  • NTFN_QOS_RELIABLE- This value specifies that reliable notification is required. Reliable notifications persist across instance and database restarts.

  • NTFN_QOS_PAYLOAD - This value specifies that payload delivery is required. It is supported only for client notification and only for RAW queues.

  • NTFN_QOS_PURGE_ON_NTFN - This value specifies that the registration is to be purged automatically when the first notification is delivered to this registration location.

ntfn_grouping_class Currently, only the following flag can be set to specify criterion for grouping. The default value will be 0. If ntfn_grouping_class is 0, all other notification grouping attributes must be 0.
  • NTFN_GROUPING_CLASS_TIME - Notifications grouped by time, that is, the user specifies a time value and a single notification gets published at the end of that time.

ntfn_grouping_value Time-period of grouping notifications specified in seconds, meaning the time after which grouping notification would be sent periodically until ntfn_grouping_repeat_count is exhausted.
ntfn_grouping_type
  • NTFN_GROUPING_TYPE_SUMMARY - Summary of all notifications that occurred in the time interval. (Default)
  • NTFN_GROUPING_TYPE_LAST - Last notification that occurred in the interval.

ntfn_grouping_start_time Notification grouping start time. Notification grouping can start from a user-specified time that should a valid timestamp with time zone. If ntfn_grouping_start_time is not specified when using grouping, the default is to current timestamp with time zone
ntfn_grouping_repeat_count Grouping notifications will be sent as many times as specified by the notification grouping repeat count and after that revert to regular notifications. The ntfn_grouping_repeat_count, if not specified, will default to
  • NTFN_GROUPING_FOREVER - Keep sending grouping notifications forever.


2.10 AQ Notification Descriptor Type

TYPE SYS.AQ$_DESCRIPTOR IS OBJECT (
   queue_name      VARCHAR2(61),
   consumer_name   VARCHAR2(30),
   msg_id          RAW(16),
   msg_prop        MSG_PROP_T,
   gen_desc        AQ$_NTFN_DESCRIPTOR,
   msgid_array     SYS.AQ$_NTFN_MSGID_ARRAY, 
   ntfnsRecdInGrp  NUMBER);

This component specifies the Oracle Streams AQ descriptor received by Oracle Streams AQ PL/SQL callbacks upon notification. It has the following attributes:

Table 2-2 AQ$_DESCRIPTOR Attributes

Attribute Description
queue_name Name of the queue in which the message was enqueued which resulted in the notification
consumer_name Name of the consumer for the multiconsumer queue
msg_id Identification number of the message
msg_prop Message properties specified by the MSG_PROP_T type
gen_desc Indicates the timeout specifications
msgid_array Group notification message ID list
ntfnsRecdInGrp Notifications received in group

2.11 AQ Message Properties Type

The message properties type msg_prop_t has the following components:

TYPE AQ$_MSG_PROP_T IS OBJECT(
   priority         number,
   delay            number,
   expiration       number,
   correlation      varchar2(128),
   attempts         number,
   recipent_list    aq$_recipient_list_t,
   exception_queue  varchar2(51),
   enqueue_time     date,
   state            number,
   sender_id        aq$_agent,
   original_misgid  raw(16),
   delivery_mode    number);


See Also:

"MESSAGE_PROPERTIES_T Type" in Oracle Database PL/SQL Packages and Types Reference

The timeout specifications type AQ$_NTFN_DESCRIPTOR has a single component:

TYPE AQ$_NTFN_DESCRIPTOR IS OBJECT(
   NTFN_FLAGS   number);

NTFN_FLAGS is set to 1 if the notifications are already removed after a stipulated timeout; otherwise the value is 0.

2.12 AQ Post Information Type

TYPE SYS.AQ$_POST_INFO IS OBJECT (
  name       VARCHAR2(128),
  namespace  NUMBER,
  payload    RAW(2000));

This component specifies anonymous subscriptions to which you want to post messages. It has three attributes:

2.13 AQ$_NTFN_MSGID_ARRAY Type

TYPE SYS.AQ$_NTFN_MSGID_ARRAY   AS VARRAY(1073741824)OF RAW(16);

This component is for storing grouping notification data for AQ namespace, value 230 which is the max varray size.

2.14 Enumerated Constants in the Oracle Streams AQ Administrative Interface

When enumerated constants such as INFINITE, TRANSACTIONAL, and NORMAL_QUEUE are selected as values, the symbol must be specified with the scope of the packages defining it. All types associated with the administrative interfaces must be prepended with DBMS_AQADM. For example:

DBMS_AQADM.NORMAL_QUEUE

Table 2-3 lists the enumerated constants in the Oracle Streams AQ administrative interface.

Table 2-3 Enumerated Constants in the Oracle Streams AQ Administrative Interface

Parameter Options
retention 0,1,2...INFINITE
message_grouping TRANSACTIONAL, NONE
queue_type NORMAL_QUEUE, EXCEPTION_QUEUE,NON_PERSISTENT_QUEUE
delivery_mode BUFFERED, PERSISTENT, PERSISTENT_OR_BUFFERED


Note:

Nonpersistent queues are deprecated in Oracle Streams AQ 10g Release 2 (10.2). Oracle recommends that you use buffered messaging instead.

2.15 Enumerated Constants in the Oracle Streams AQ Operational Interface

When using enumerated constants such as BROWSE, LOCKED, and REMOVE, the PL/SQL constants must be specified with the scope of the packages defining them. All types associated with the operational interfaces must be prepended with DBMS_AQ. For example:

DBMS_AQ.BROWSE

Table 2-4 lists the enumerated constants in the Oracle Streams AQ operational interface.

Table 2-4 Enumerated Constants in the Oracle Streams AQ Operational Interface

Parameter Options
visibility IMMEDIATE, ON_COMMIT
dequeue mode BROWSE, LOCKED, REMOVE, REMOVE_NODATA
navigation FIRST_MESSAGE, NEXT_MESSAGE, NEXT_TRANSACTION
state WAITING, READY, PROCESSED, EXPIRED
wait FOREVER, NO_WAIT
delay NO_DELAY
expiration NEVER
namespace NAMESPACE_AQ, NAMESPACE_ANONYMOUS
delivery_mode BUFFERED, PERSISTENT, PERSISTENT_OR_BUFFERED
quosflags NTFN_QOS_RELIABLE, NTFN_QOS_PAYLOAD, NTFN_QOS_PURGE_ON_NTFN
ntfn_grouping_class NFTN_GROUPING_CLASS_TIME
ntfn_grouping_type NTFN_GROUPING_TYPE_SUMMARY, NTFN_GROUPING_TYPE_LAST
ntfn_grouping_repeat_count NTFN_GROUPING_FOREVER

2.16 AQ Background Processes

2.16.1 Queue Monitor Processes

A number of Streams AQ or Streams tasks are executed in the background. These include converting messages with DELAY specified into the READY state, expiring messages, moving messages to exception queues, spilling and recovering of buffered messages, and similar operations.

These are executed by a set of AQ background process. These include a coordinator process, name QMNC (link), which dynamically spawns subordinate processes Qxx as needed. The number of subordinate processes is determined automatically and tuned constantly.

It is no longer necessary to set AQ_TM_PROCESSES when Oracle Streams AQ or Streams is used. If a value is specified, that value is taken into account when starting the Qxx processes. However, the number of Qxx processes can be different from what was specified by AQ_TM_PROCESSES.

QMNC only runs when you use queues and create new queues. It affects Streams Replication and Messaging users.

No separate API is needed to disable or enable the background processes. This is controlled by setting AQ_TM_PROCESSES to zero or nonzero. Oracle recommends, however, that you leave the AQ_TM_PROCESSES parameter unspecified and let the system autotune.


Note:

If you want to disable the Queue Monitor Coordinator, then you must set AQ_TM_PROCESSES = 0 in your pfile or spfile. Oracle strongly recommends that you do NOT set AQ_TM_PROCESSES = 0. If you are using Oracle Streams, then setting this parameter to zero (which Oracle Database respects no matter what) can cause serious problems.

2.16.2 Job Queue Processes

Propagation and PL/SQL notifications are handled by job queue (Jnnn) processes. The parameter JOB_QUEUE_PROCESSES no longer needs to be specified. The database scheduler automatically starts the job queue processes that are needed for the propagation and notification jobs.