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Oracle® Database Advanced Queuing User's Guide
12c Release 1 (12.1)

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2 Basic Components

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

This chapter contains the following topics:

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.

Type Name

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

This component defines queue types. The maximum number of attributes in the object type is limited to 900.

To store payloads of type RAW, Oracle Database Advanced Queuing 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 Database Advanced Queuing 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.

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:

  • name

    This attribute specifies the name of a producer or consumer of a message. It can be the name of an application or a name assigned by an application. A queue can itself be an agent, enqueuing or dequeuing from another queue. The name must follow the reserved character guidelines in Oracle Database SQL Language Reference.

  • address

    This attribute is interpreted in the context of protocol. If protocol is 0 (default), then address is of the form [schema.]queue[@dblink].

  • protocol

    This attribute specifies the protocol to interpret the address and propagate the message. The default value is 0.

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.

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.

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.

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.

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.

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 Database Advanced Queuing 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 Database 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.


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 Database Advanced Queuing descriptor received by Oracle Database Advanced Queuing 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


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.

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:

  • name

    This attribute specifies the name of the anonymous subscription to which you want to post.

  • namespace

    This attribute specifies the namespace of the anonymous subscription. To receive notifications from other applications using DBMS_AQ.POST or OCISubscriptionPost(), the namespace must be DBMS_AQ.NAMESPACE_ANONYMOUS.

  • payload

    This attribute specifies the payload to be posted to the anonymous subscription. The default is NULL.

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.

Enumerated Constants for 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 Database Advanced Queuing administrative interface.

Table 2-3 Enumerated Constants in the Oracle Database Advanced Queuing 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 Database Advanced Queuing 10g Release 2 (10.2). Oracle recommends that you use buffered messaging instead.

Enumerated Constants for 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 Database Advanced Queuing operational interface.

Table 2-4 Enumerated Constants in the Oracle Database Advanced Queuing 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


AQ Background Processes

Queue Monitor Processes

Many 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.

It is no longer necessary to set AQ_TM_PROCESSES when Oracle Database 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.

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.

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.

AQ Background Architecture

Oracle Database Advanced Queuing 12c Release 1 (12.1) introduces a new AQ background architecture with a 3-tier design:

  • Tier1 (AQPC): Asingle background process called the Advanced Queueing Process Coordinator is created at instance startup. It will be responsible for creating and managing various master processes. The coordinator statistics can be viewed using GV$AQ_BACKGROUND_COORDINATOR.

  • Tier2 (QM**): There will be many master processes named Queue Monitors. Each will be responsible for handling a distinct type of job. Jobs could be of type notification(Emon pool), queue monitors (handling sharded queues time manager etc) , cross process etc.

    Note:

    The old processes like QMNC and EMNC will be subsumed within one of new master processes.

    A job can be defined as a type of work which needs own scheduling mechanism across multiple server processes (Q***) to perform its task . The master process statistics and their jobs can be viewed using GV$AQ_JOB_COORDINATOR.

  • Tier3(Q***): There will be a single pool of server processes for all above mentioned master processes. Each process will be associated to a single master process at a time. But can be rescheduled to another once original master relinquishes its need to use it.These servers will perform jobs for respective masters providing performance and scalability. The server process statistics and its current master association can be viewed using GV$AQ_SERVER_POOL.