Data Structures for DBMS_AQ

Table 5-2  Data Structures for DBMS_AQ

Data Structures
Object Name
Type Name
AQ PL/SQL Callback

Object Name

The object_name data structure names database objects. It applies to queues, queue tables, agent names, and object types.

Syntax

object_name := VARCHAR2;
object_name := [<schema_name>.]<name>;

Usage Notes

Names for objects are specified by an optional schema name and a name. If the schema name is not specified, the current schema is assumed. The name must follow object name guidelines in the Oracle9i SQL Reference with regard to reserved characters. Schema names, agent names, and object type names can be up to 30 bytes long. Queue names and queue table names can be up to 24 bytes long.

Type Name

The type_name data structure defines queue types.

Syntax

type_name := VARCHAR2;
type_name := <object_type> | "RAW";

Attributes

Table 5-3  Type Name Attributes

Attribute	Description
<object_types>	Maximum number of attributes in the object type is limited to 900.
"RAW"	To store payload of type RAW, AQ creates a queue table with a LOB column as the payload repository. The theoretical maximum size of the message payload is the maximum amount of data that can be stored in a LOB column. However, the maximum size of the payload is determined by which programmatic environment you use to access AQ. For PL/SQL, Java and precompilers the limit is 32K; for the OCI the limit is 4G. Because the PL/SQL enqueue and dequeue interfaces accept RAW buffers as the payload parameters you will be limited to 32K bytes. In OCI, the maximum size of your RAW data will be limited to the maximum amount of contiguous memory (as an OCIRaw is simply an array of bytes) that the OCI Object Cache can allocate. Typically, this will be at least 32K bytes and much larger in many cases. Because LOB columns are used for storing RAW payload, the 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.

AQ PL/SQL Callback

The plsqlcallback data structure specifies the user-defined PL/SQL procedure, defined in the database to be invoked on message notification.

Syntax

If a notification message is expected for a RAW payload enqueue, then the PL/SQL callback must have the following signature:

procedure plsqlcallback(
  context  IN  RAW, 
  reginfo  IN  SYS.AQ$_REG_INFO, 
  descr    IN  SYS.AQ$_DESCRIPTOR, 
  payload  IN  RAW,
  payloadl IN  NUMBER);

Attributes

Table 5-4  AQ PL/SQL Callback Attributes

Attribute	Description
context	Specifies the context for the callback function that was passed by dbms_aq.register. See "AQ$_REG_INFO Type".
reginfo	See "AQ$_REG_INFO Type".
descr	See "AQ$_DESCRIPTOR Type".
payload	If a notification message is expected for a raw payload enqueue then this contains the raw payload that was enqueued into a non persistent queue. In case of a persistent queue with raw payload this parameter will be null.
payloadl	Specifies the length of payload. If payload is null, payload1 = 0.

If the notification message is expected for an ADT payload enqueue, the PL/SQL callback must have the following signature:

procedure plsqlcallback(
  context  IN RAW, 
  reginfo  IN SYS.AQ$_REG_INFO, 
  descr    IN SYS.AQ$_DESCRIPTOR, 
  payload  IN VARCHAR2,
  payloadl IN NUMBER);