2 Basic Components of Oracle Database Advanced Queuing
This topic lists the basic components of Oracle Database Advanced Queuing.
2.1 Object Name
This component names database objects.
object_name := VARCHAR2 object_name := [schema_name.]name
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 ReferenceOracle Database SQL Language Reference. The schema name, agent name, and the object type name can each be up to 128 bytes long. However starting from 12c Release 2 (12.2.), queue names and queue table names can be a maximum of 122 bytes.
2.2 Type Name
This component defines queue types.
type_name := VARCHAR2
type_name := object_type | "RAW"
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.
2.3 AQ Agent Type
This component identifies a producer or consumer of a message.
TYPE AQ$_AGENT IS OBJECT ( name VARCHAR2(30), address VARCHAR2(1024), protocol NUMBER);
All consumers that are added as subscribers to a multiconsumer queue must have unique values for the AQ$_AGENT
parameters. Two subscribers cannot have the same values for the NAME
, ADDRESS,
and PROTOCOL
attributes for the AQ$_AGENT
type. At least one of the three attributes must be different for two subscribers.
You can add subscribers by repeatedly using the DBMS_AQADM.ADD_SUBSCRIBER
procedure up to a maximum of 1024 subscribers for a multiconsumer queue.
This type has three attributes:
-
name
This attribute specifies the name of a producer or a consumer of a message. It can be the name of an application or a name assigned by an application. A queue can itself be an agent, enqueuing or dequeuing from another queue. The name must follow the reserved character guidelines in Oracle Database SQL Language Reference.
-
address
This attribute is interpreted in the context of
protocol
. Ifprotocol
is 0 (default), thenaddress
is of the form[schema.]queue[@dblink]
. -
protocol
This attribute specifies the protocol to interpret the address and propagate the message. The default value is 0.
2.4 AQ Recipient List Type
This component identifies the list of agents that receive a message.
TYPE AQ$_RECIPIENT_LIST_T IS TABLE OF aq$_agent INDEX BY BINARY_INTEGER;
2.5 AQ Agent List Type
This component identifies the list of agents for DBMS_AQ.LISTEN
to listen for.
TYPE AQ$_AGENT_LIST_T IS TABLE OF aq$_agent INDEX BY BINARY INTEGER;
2.6 AQ Subscriber List Type
This component identifies the list of subscribers that subscribe to this queue.
TYPE AQ$_SUBSCRIBER_LIST_T IS TABLE OF aq$_agent INDEX BY BINARY INTEGER;
2.7 AQ Registration Information List Type
This component identifies the list of registrations to a queue.
TYPE AQ$_REG_INFO_LIST AS VARRAY(1024) OF sys.aq$_reg_info;
2.8 AQ Post Information List Type
This component identifies the list of anonymous subscriptions to which messages are posted.
TYPE AQ$_POST_INFO_LIST AS VARRAY(1024) OF sys.aq$_post_info;
2.9 AQ Registration Information Type
This component identifies a producer or a consumer of a message.
TYPE SYS.AQ$_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);
Its attributes are described in the following list.
Table 2-1 AQ$_REG_INFO Type Attributes
Attribute | Description |
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Specifies the name of the subscription. The subscription name is of the form |
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Specifies the namespace of the subscription. To receive notification from Oracle Database AQ queues, the namespace must be |
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Specifies the action to be performed on message notification. For HTTP notifications, use |
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Specifies the context that is to be passed to the callback function |
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Can be set to one or more of the following values to specify the notification quality of service:
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Currently, only the following flag can be set to specify criterion for grouping. The default value will be 0. If
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Time-period of grouping notifications specified in seconds, meaning the time after which grouping notification would be sent periodically until |
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Notification grouping start time. Notification grouping can start from a user-specified time that should a valid timestamp with time zone. If |
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Grouping notifications will be sent as many times as specified by the notification grouping repeat count and after that revert to regular notifications. The ntfn_grouping_repeat_count, if not specified, will default to
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2.10 AQ Notification Descriptor Type
This component specifies the Oracle Database Advanced Queuing descriptor received by AQ PL/SQL callbacks upon notification.
TYPE SYS.AQ$_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);
It has the following attributes:
Table 2-2 AQ$_DESCRIPTOR Attributes
Attribute | Description |
---|---|
|
Name of the queue in which the message was enqueued which resulted in the notification |
|
Name of the consumer for the multiconsumer queue |
|
Identification number of the message |
|
Message properties specified by the |
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Indicates the timeout specifications |
|
Group notification message ID list |
|
Notifications received in group |
2.11 AQ Message Properties Type
The message properties type msg_prop_t
has these components.
TYPE AQ$_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);
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
.
See Also:
"MESSAGE_PROPERTIES_T Type" in Oracle Database PL/SQL Packages and Types Reference
2.12 AQ Post Information Type
This component specifies anonymous subscriptions to which you want to post messages.
TYPE SYS.AQ$_POST_INFO IS OBJECT ( name VARCHAR2(128), namespace NUMBER, payload RAW(2000));
It has three attributes:
-
name
This attribute specifies the name of the anonymous subscription to which you want to post.
-
namespace
This attribute specifies the namespace of the anonymous subscription. To receive notifications from other applications using
DBMS_AQ.POST
orOCISubscriptionPost()
, the namespace must beDBMS_AQ.NAMESPACE_ANONYMOUS
. -
payload
This attribute specifies the payload to be posted to the anonymous subscription. The default is
NULL
.
2.13 AQ$_NTFN_MSGID_ARRAY Type
This component is for storing grouping notification data for AQ namespace, value 230 which is the max varray size.
TYPE SYS.AQ$_NTFN_MSGID_ARRAY AS VARRAY(1073741824)OF RAW(16);
2.14 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 |
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Note:
Nonpersistent queues are deprecated in Oracle Database Advanced Queuing 10g Release 2 (10.2). Oracle recommends that you use buffered messaging instead.
2.15 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 |
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2.16 AQ Background Processes
These topics describe the background processes of Oracle Database Advanced Queuing.
2.16.1 Queue Monitor Processes
Oracle recommends leaving the AQ_TM_PROCESSES
parameter unspecified and let the system autotune.
Many Oracle Database Advanced Queuing 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 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.
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.
2.16.3 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
.