Oracle Built−in Packages- P31: Ah, for the good old days of Version of PL /SQL! Life was so simple then. No stored procedures or functions and certainly no packages. You had your set of built−in functions, like SUBSTR and TO_DATE. You had the IF statement and various kinds of loops. With these tools at hand, you built your batch−processing scripts for execution in SQL*Plus, and you coded your triggers in SQL*Forms , and you went home at night content with a good day's work done. | Appendix A What s on the Companion Disk REMOVE_PIPE Removes the named pipe Yes RESET_BUFFER Resets buffer message pointers No SEND_MESSAGE Sends local message buffer out on pipe Yes UNIQUE_SESSION_NAME Returns string unique to the session Yes UNPACK_MESSAGE Unpacks item from message buffer No UNPACK_MESSAGE_RAW Unpacks RAW item from message buffer No UNPACK_MESSAGE_ROWID Unpacks ROWID item from message buffer No DBMS_PIPE does not declare any package exceptions of its own. Many of the individual programs raise Oracle exceptions under certain circumstances as described in the following sections. DBMS_PIPE nonprogram elements The DBMS_PIPE package contains one nonprogram element maxwait. It is defined as follows maxwait CONSTANT INTEGER 86400000 The maxwait constant is used as the default maximum time to wait for calls to the SEND_MESSAGE or RECEIVE_MESSAGE functions to complete. The units are in seconds so the value of 86400000 equates to 1000 days. How Database Pipes Work It is important to understand how DBMS_PIPE implements the concept of a communications pipe between Oracle sessions and this implementation is not necessarily obvious. Memory structures The pipes themselves are named memory areas in the Oracle SGA s shared pool where communications messages can be written or read. DBMS_PIPE works through the interaction of these memory areas with a private memory buffer in each user s session. There is only one private memory buffer per user that is used to send and receive messages on database pipes. Private buffers can be thought of as mailboxes one for each user and the database pipes are like the post office. The difference is that users are responsible for delivering and retrieving messages to and from the post office. 1 1 Dan Clamage technical reviewer extraordinaire points out that the single-session message buffer is actually implemented as a private global variable in the DBMS_PIPE package body. He laments and I join him that Oracle
