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ANYDATA Queues and User Messages

原创 Linux操作系统 作者:zhouxianwang 时间:2012-06-23 16:25:38 0 删除 编辑

Streams enables messaging with queues of type ANYDATA. These queues can stage user messages whose payloads are of ANYDATA type. An ANYDATA payload can be a wrapper for payloads of different datatypes.

By using ANYDATA wrappers for message payloads, publishing applications can enqueue messages of different types into a single queue, and subscribing applications can dequeue these messages, either explicitly using a messaging client or an application, or implicitly using an apply process. If the subscribing application is remote, then the messages can be propagated to the remote site, and the subscribing application can dequeue the messages from a local queue in the remote database. Alternatively, a remote subscribing application can dequeue messages directly from the source queue using a variety of standard protocols, such as PL/SQL and OCI.

Streams includes the features of Advanced Queuing (AQ), which supports all the standard features of message queuing systems, including multiconsumer queues, publish and subscribe, content-based routing, internet propagation, transformations, and gateways to other messaging subsystems.

You can wrap almost any type of payload in an ANYDATA payload. To do this, you use the Convertdata_type static functions of the ANYDATA type, where data_type is the type of object to wrap. These functions take the object as input and return an ANYDATA object.

You cannot enqueue ANYDATA payloads that contain payloads of the following types into an ANYDATA queue:

  • CLOB


  • BLOB

  • Object types with LOB attributes

  • Object types that use type evolution or type inheritance


  • Payloads of ROWID datatype cannot be wrapped in an ANYDATA wrapper. This restriction does not apply to payloads of UROWID datatype.

  • A queue that can stage messages of only one particular type is called a typed queue.

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