Oracle provides the DBMS_OUTPUT package to give you a way to send information from your programs to a buffer. This buffer can then be read and manipulated by another PL/SQL program or by the host environment. DBMS_OUTPUT is most frequently used as a simple mechanism for displaying information on your screen.
Each user session has a DBMS_OUTPUT buffer of predefined size, which developers commonly set to UNLIMITED. Oracle versions prior to Oracle Database 10g Release 2 had a 1 million-byte limit. Once filled, you will need to empty it before you can reuse it; you can empty it programmatically, but more commonly you will rely on the host environment (such as SQL*Plus) to empty it and display its contents. This only occurs after the outermost PL/SQL block terminates; you cannot use DBMS_OUTPUT for real-time streaming of messages from your program.
The way to write information to this buffer is by calling the DBMS_OUTPUT.PUT and DBMS_OUTPUT.PUT_LINE programs. If you want to read from the buffer programmatically, you can use DBMS_OUTPUT.GET_LINE or DBMS_OUTPUT.GET_LINES.
Since the default setting of DBMS_OUTPUT is disabled, calls to the PUT_LINE and PUT programs are ignored and the buffer remains empty. To enable DBMS_OUTPUT, you generally execute a command in the host environment. For example, in SQL*Plus, you can issue this command:
SET SERVEROUTPUT ON SIZE UNLIMITED
In addition to enabling output to the console, this command has the side effect ...