The DBMS_OUTPUT
package enables you to send messages from stored procedures, packages, and triggers. The package is especially useful for displaying PL/SQL debugging information.
This chapter contains the following topics:
Overview
Security Model
Operational Notes
Exceptions
Rules and Limits
Examples
TABLE Types
OBJECT Types
This section contains topics which relate to using the DBMS_OUTPUT
package.
The package is typically used for debugging, or for displaying messages and reports to SQL*DBA or SQL*Plus (such as are produced by applying the SQL command DESCRIBE
to procedures).
The PUT Procedure and PUT_LINE Procedure in this package enable you to place information in a buffer that can be read by another trigger, procedure, or package. In a separate PL/SQL procedure or anonymous block, you can display the buffered information by calling the GET_LINE Procedure and GET_LINES Procedure.
If the package is disabled, all calls to subprograms are ignored. In this way, you can design your application so that subprograms are available only when a client is able to process the information.
The dbmsotpt.sql
script must be run as user SYS
. This creates the public synonym DBMS_OUTPUT
, and EXECUTE
permission on this package is granted to public
.
If you do not call GET_LINE
, or if you do not display the messages on your screen in SQL*Plus, the buffered messages are ignored.
SQL*Plus calls GET_LINES
after issuing a SQL statement or anonymous PL/SQL calls.
Typing SET
SERVEROUTPUT
ON
in SQL*Plus has the effect of invoking
DBMS_OUTPUT.ENABLE (buffer_size => NULL);
with no limit on the output.
You should generally avoid having application code invoke either the DISABLE Procedure or ENABLE Procedure because this could subvert the attempt of an external tool like SQL*Plus to control whether or not to display output.
Note:
Messages sent usingDBMS_OUTPUT
are not actually sent until the sending subprogram or trigger completes. There is no mechanism to flush output during the execution of a procedure.DBMS_OUTPUT
subprograms raise the application error ORA-20000
, and the output procedures can return the following errors:
Error | Description |
---|---|
|
Buffer overflow |
|
Line length overflow |
The maximum line size is 32767 bytes.
The default buffer size is 20000 bytes. The minimum size is 2000 bytes and the maximum is unlimited.
Example 1: Using a Trigger to Produce Output
You can use a trigger to print out some output from the debugging process. For example, you could code the trigger to invoke:
DBMS_OUTPUT.PUT_LINE('I got here:'||:new.col||' is the new value');
If you have enabled the DBMS_OUTPUT
package, then the text produced by this PUT_LINE
would be buffered, and you could, after executing the statement (presumably some INSERT
, DELETE
, or UPDATE
that caused the trigger to fire), retrieve the line of information. For example:
BEGIN DBMS_OUTPUT.GET_LINE(:buffer, :status); END;
You could then optionally display the buffer on the screen. You repeat calls to GET_LINE
until status
comes back as nonzero. For better performance, you should use calls to GET_LINES Procedure which can return an array of lines.
Example 2: Debugging Stored Procedures and Triggers
The DBMS_OUTPUT
package is commonly used to debug stored procedures and triggers. This package can also be used to enable you to retrieve information about an object and format this output, as shown in "Example 3: Retrieving Information About an Object".
This function queries the employee table and returns the total salary for a specified department. The function includes several calls to the PUT_LINE
procedure:
CREATE FUNCTION dept_salary (dnum NUMBER) RETURN NUMBER IS CURSOR emp_cursor IS SELECT sal, comm FROM emp WHERE deptno = dnum; total_wages NUMBER(11, 2) := 0; counter NUMBER(10) := 1; BEGIN FOR emp_record IN emp_cursor LOOP emp_record.comm := NVL(emp_record.comm, 0); total_wages := total_wages + emp_record.sal + emp_record.comm; DBMS_OUTPUT.PUT_LINE('Loop number = ' || counter || '; Wages = '|| TO_CHAR(total_wages)); /* Debug line */ counter := counter + 1; /* Increment debug counter */ END LOOP; /* Debug line */ DBMS_OUTPUT.PUT_LINE('Total wages = ' || TO_CHAR(total_wages)); RETURN total_wages; END dept_salary;
Assume the EMP
table contains the following rows:
EMPNO SAL COMM DEPT ----- ------- -------- ------- 1002 1500 500 20 1203 1000 30 1289 1000 10 1347 1000 250 20
Assume the user executes the following statements in SQL*Plus:
SET SERVEROUTPUT ON VARIABLE salary NUMBER; EXECUTE :salary := dept_salary(20);
The user would then see the following information displayed in the output pane:
Loop number = 1; Wages = 2000 Loop number = 2; Wages = 3250 Total wages = 3250 PL/SQL procedure successfully executed.
Example 3: Retrieving Information About an Object
In this example, the user has used the EXPLAIN
PLAN
command to retrieve information about the execution plan for a statement and has stored it in PLAN_TABLE
. The user has also assigned a statement ID to this statement. The example EXPLAIN_OUT
procedure retrieves the information from this table and formats the output in a nested manner that more closely depicts the order of steps undergone in processing the SQL statement.
/****************************************************************/ /* Create EXPLAIN_OUT procedure. User must pass STATEMENT_ID to */ /* to procedure, to uniquely identify statement. */ /****************************************************************/ CREATE OR REPLACE PROCEDURE explain_out (statement_id IN VARCHAR2) AS -- Retrieve information from PLAN_TABLE into cursor EXPLAIN_ROWS. CURSOR explain_rows IS SELECT level, id, position, operation, options, object_name FROM plan_table WHERE statement_id = explain_out.statement_id CONNECT BY PRIOR id = parent_id AND statement_id = explain_out.statement_id START WITH id = 0 ORDER BY id; BEGIN -- Loop through information retrieved from PLAN_TABLE: FOR line IN explain_rows LOOP -- At start of output, include heading with estimated cost. IF line.id = 0 THEN DBMS_OUTPUT.PUT_LINE ('Plan for statement ' || statement_id || ', estimated cost = ' || line.position); END IF; -- Output formatted information. LEVEL determines indention level. DBMS_OUTPUT.PUT_LINE (lpad(' ',2*(line.level-1)) || line.operation || ' ' || line.options || ' ' || line.object_name); END LOOP; END;
See Also:
Chapter 168, "UTL_FILE"The DBMS_OUTPUT
package declares 2 collection types for use with the GET_LINES Procedure.
DBMSOUTPUT_LINESARRAY Object Type
This package type is to be used with the GET_LINES Procedure to obtain text submitted through the PUT Procedure and PUT_LINE Procedure.
TYPE CHARARR IS TABLE OF VARCHAR2(32767) INDEX BY BINARY_INTEGER;
This package type is to be used with the GET_LINES Procedure to obtain text submitted through the PUT Procedure and PUT_LINE Procedure.
TYPE DBMSOUTPUT_LINESARRAY IS VARRAY(2147483647) OF VARCHAR2(32767);
Table 68-2 DBMS_OUTPUT Package Subprograms
Subprogram | Description |
---|---|
Disables message output |
|
Enables message output |
|
Retrieves one line from buffer |
|
Retrieves an array of lines from buffer |
|
Terminates a line created with |
|
Places a line in the buffer |
|
Places partial line in buffer |
Note:
The PUT Procedure that take a number are obsolete and, while currently supported, are included in this release for legacy reasons only.This procedure disables calls to PUT
, PUT_LINE
, NEW_LINE
, GET_LINE
, and GET_LINES
, and purges the buffer of any remaining information.
As with the ENABLE Procedure, you do not need to call this procedure if you are using the SERVEROUTPUT
option of SQL*Plus.
DBMS_OUTPUT.DISABLE;
pragma restrict_references(disable,WNDS,RNDS);
This procedure enables calls to PUT
, PUT_LINE
, NEW_LINE
, GET_LINE
, and GET_LINES
. Calls to these procedures are ignored if the DBMS_OUTPUT
package is not activated.
DBMS_OUTPUT.ENABLE ( buffer_size IN INTEGER DEFAULT 20000);
pragma restrict_references(enable,WNDS,RNDS);
Table 68-3 ENABLE Procedure Parameters
Parameter | Description |
---|---|
|
Upper limit, in bytes, the amount of buffered information. Setting |
It is not necessary to call this procedure when you use the SET
SERVEROUTPUT
option of SQL*Plus.
If there are multiple calls to ENABLE
, then buffer_size
is the last of the values specified. The maximum size is 1,000,000, and the minimum is 2,000 when the user specifies buffer_size
(NOT
NULL
).
NULL
is expected to be the usual choice. The default is 20,000 for backwards compatibility with earlier database versions that did not support unlimited buffering.
This procedure retrieves a single line of buffered information.
DBMS_OUTPUT.GET_LINE ( line OUT VARCHAR2, status OUT INTEGER);
Table 68-4 GET_LINE Procedure Parameters
Parameter | Description |
---|---|
|
Returns a single line of buffered information, excluding a final newline character. You should declare the actual for this parameter as |
|
If the call completes successfully, then the status returns as 0. If there are no more lines in the buffer, then the status is 1. |
You can choose to retrieve from the buffer a single line or an array of lines. Call the GET_LINE
procedure to retrieve a single line of buffered information. To reduce the number of calls to the server, call the GET_LINES
procedure to retrieve an array of lines from the buffer.
You can choose to automatically display this information if you are using SQL*Plus by using the special SET
SERVEROUTPUT
ON
command.
After calling GET_LINE
or GET_LINES
, any lines not retrieved before the next call to PUT
, PUT_LINE
, or NEW_LINE
are discarded to avoid confusing them with the next message.
This procedure retrieves an array of lines from the buffer.
DBMS_OUTPUT.GET_LINES ( lines OUT CHARARR, numlines IN OUT INTEGER); DBMS_OUTPUT.GET_LINES ( lines OUT DBMSOUTPUT_LINESARRAY, numlines IN OUT INTEGER);
Table 68-5 GET_LINES Procedure Parameters
Parameter | Description |
---|---|
|
Returns an array of lines of buffered information. The maximum length of each line in the array is 32767 bytes. It is recommended that you use the |
|
Number of lines you want to retrieve from the buffer. After retrieving the specified number of lines, the procedure returns the number of lines actually retrieved. If this number is less than the number of lines requested, then there are no more lines in the buffer. |
You can choose to retrieve from the buffer a single line or an array of lines. Call the GET_LINE
procedure to retrieve a single line of buffered information. To reduce the number of calls to the server, call the GET_LINES
procedure to retrieve an array of lines from the buffer.
You can choose to automatically display this information if you are using SQL*Plus by using the special SET
SERVEROUTPUT
ON
command.
After calling GET_LINE
or GET_LINES
, any lines not retrieved before the next call to PUT
, PUT_LINE
, or NEW_LINE
are discarded to avoid confusing them with the next message.
This procedure puts an end-of-line marker. The GET_LINE Procedure and the GET_LINES Procedure return "lines" as delimited by "newlines". Every call to the PUT_LINE Procedure or NEW_LINE Procedure generates a line that is returned by GET_LINE
(S
).
DBMS_OUTPUT.NEW_LINE;
This procedure places a partial line in the buffer.
Note:
ThePUT
procedure that takes a NUMBER
is obsolete and, while currently supported, is included in this release for legacy reasons only.DBMS_OUTPUT.PUT ( item IN VARCHAR2);
Table 68-7 PUT and PUT_LINE Procedure Exceptions
Error | Description |
---|---|
|
Buffer overflow, limit of < |
|
Line length overflow, limit of 32767 bytes for each line. |
You can build a line of information piece by piece by making multiple calls to PUT
, or place an entire line of information into the buffer by calling PUT_LINE
.
When you call PUT_LINE
the item you specify is automatically followed by an end-of-line marker. If you make calls to PUT
to build a line, then you must add your own end-of-line marker by calling NEW_LINE
. GET_LINE
and GET_LINES
do not return lines that have not been terminated with a newline character.
If your lines exceed the line limit, you receive an error message.
Output that you create using PUT
or PUT_LINE
is buffered. The output cannot be retrieved until the PL/SQL program unit from which it was buffered returns to its caller.
For example, SQL*Plus does not display DBMS_OUTPUT
messages until the PL/SQL program completes. There is no mechanism for flushing the DBMS_OUTPUT
buffers within the PL/SQL program.
SQL> SET SERVEROUTPUT ON SQL> BEGIN 2 DBMS_OUTPUT.PUT_LINE ('hello'); 3 DBMS_LOCK.SLEEP (10); 4 END;
This procedure places a line in the buffer.
Note:
ThePUT_LINE
procedure that takes a NUMBER
is obsolete and, while currently supported, is included in this release for legacy reasons only.DBMS_OUTPUT.PUT_LINE ( item IN VARCHAR2);
Table 68-9 PUT and PUT_LINE Procedure Exceptions
Error | Description |
---|---|
|
Buffer overflow, limit of < |
|
Line length overflow, limit of 32767 bytes for each line. |
You can build a line of information piece by piece by making multiple calls to PUT
, or place an entire line of information into the buffer by calling PUT_LINE
.
When you call PUT_LINE
the item you specify is automatically followed by an end-of-line marker. If you make calls to PUT
to build a line, then you must add your own end-of-line marker by calling NEW_LINE
. GET_LINE
and GET_LINES
do not return lines that have not been terminated with a newline character.
If your lines exceeds the line limit, you receive an error message.
Output that you create using PUT
or PUT_LINE
is buffered. The output cannot be retrieved until the PL/SQL program unit from which it was buffered returns to its caller.
For example, SQL*Plus does not display DBMS_OUTPUT
messages until the PL/SQL program completes. There is no mechanism for flushing the DBMS_OUTPUT
buffers within the PL/SQL program. For example:
SQL> SET SERVEROUTPUT ON SQL> BEGIN 2 DBMS_OUTPUT.PUT_LINE ('hello'); 3 DBMS_LOCK.SLEEP (10); 4 END;