DBMS_AQ v16
EDB Postgres Advanced Server Advanced Queueing provides message queueing and message processing for the EDB Postgres Advanced Server database. User-defined messages are stored in a queue, and a collection of queues is stored in a queue table. Procedures in the DBMS_AQADM package create and manage message queues and queue tables. Use the DBMS_AQ package to add messages to or remove them from a queue or to register or unregister a PL/SQL callback procedure.
EDB Postgres Advanced Server also provides extended (noncompatible) functionality for the DBMS_AQ package with SQL commands. See SQL reference for detailed information about the following SQL commands:
ALTER QUEUEALTER QUEUE TABLECREATE QUEUECREATE QUEUE TABLEDROP QUEUEDROP QUEUE TABLE
The DBMS_AQ package provides procedures that allow you to enqueue a message, dequeue a message, and manage callback procedures. The supported procedures are:
| Function/procedure | Return type | Description |
|---|---|---|
ENQUEUE | n/a | Post a message to a queue. |
DEQUEUE | n/a | Retrieve a message from a queue if or when a message is available. |
REGISTER | n/a | Register a callback procedure. |
UNREGISTER | n/a | Unregister a callback procedure. |
EDB Postgres Advanced Server's implementation of DBMS_AQ is a partial implementation when compared to Oracle's version. Only those procedures listed in the table above are supported.
EDB Postgres Advanced Server supports use of these constants:
| Constant | Description | For parameters |
|---|---|---|
DBMS_AQ.BROWSE (0) | Read the message without locking. | dequeue_options_t.dequeue_mode |
DBMS_AQ.LOCKED (1) | This constant is defined but returns an error if used. | dequeue_options_t.dequeue_mode |
DBMS_AQ.REMOVE (2) | Delete the message after reading (the default). | dequeue_options_t.dequeue_mode |
DBMS_AQ.REMOVE_NODATA (3) | This constant is defined but returns an error if used. | dequeue_options_t.dequeue_mode |
DBMS_AQ.FIRST_MESSAGE (0) | Return the first available message that matches the search terms. | dequeue_options_t.navigation |
DBMS_AQ.NEXT_MESSAGE (1) | Return the next available message that matches the search terms. | dequeue_options_t.navigation |
DBMS_AQ.NEXT_TRANSACTION (2) | This constant is defined but returns an error if used. | dequeue_options_t.navigation |
DBMS_AQ.FOREVER (-1) | Wait forever if a message that matches the search term isn't found (the default). | dequeue_options_t.wait |
DBMS_AQ.NO_WAIT (0) | Don't wait if a message that matches the search term isn't found. | dequeue_options_t.wait |
DBMS_AQ.ON_COMMIT (0) | The dequeue is part of the current transaction. | enqueue_options_t.visibility, dequeue_options_t.visibility |
DBMS_AQ.IMMEDIATE (1) | This constant is defined but returns an error if used. | enqueue_options_t.visibility, dequeue_options_t.visibility |
DBMS_AQ.PERSISTENT (0) | Store the message in a table. | enqueue_options_t.delivery_mode |
DBMS_AQ.BUFFERED (1) | This constant is defined but returns an error if used. | enqueue_options_t.delivery_mode |
DBMS_AQ.READY (0) | Specifies that the message is ready to process. | message_properties_t.state |
DBMS_AQ.WAITING (1) | Specifies that the message is waiting to be processed. | message_properties_t.state |
DBMS_AQ.PROCESSED (2) | Specifies that the message was processed. | message_properties_t.state |
DBMS_AQ.EXPIRED (3) | Specifies that the message is in the exception queue. | message_properties_t.state |
DBMS_AQ.NO_DELAY (0) | This constant is defined but returns an error if used. | message_properties_t.delay |
DBMS_AQ.NEVER (NULL) | This constant is defined but returns an error if used. | message_properties_t.expiration |
DBMS_AQ.NAMESPACE_AQ (0) | Accept notifications from DBMS_AQ queues. | sys.aq$_reg_info.namespace |
DBMS_AQ.NAMESPACE_ANONYMOUS (1) | This constant is defined but returns an error if used. | sys.aq$_reg_info.namespace |
The DBMS_AQ configuration parameters listed in the following table can be defined in the postgresql.conf file. After the configuration parameters are defined, you can invoke the DBMS_AQ package to use and manage messages held in queues and queue tables.
| Parameter | Description |
|---|---|
dbms_aq.max_workers | The maximum number of workers to run. |
dbms_aq.max_idle_time | The idle time a worker must wait before exiting. |
dbms_aq.min_work_time | The minimum time a worker can run before exiting. |
dbms_aq.launch_delay | The minimum time between creating workers. |
dbms_aq.batch_size | The maximum number of messages to process in a single transaction. The default batch size is 10. |
dbms_aq.max_databases | The size of the DBMS_AQ hash table of databases. The default value is 1024. |
dbms_aq.max_pending_retries | The size of the DBMS_AQ hash table of pending retries. The default value is 1024. |
enqueue dequeue register unregister