Monitoring long-running PL/SQL block

Question

I have a fairly time intensive PL/SQL block that builds fingerprints from molecular structures. I would like to print output to SQL*Plus console to provide feedback on how many structures have been processed. I can do this with dbms_output.put_line

However everytime that is called a new line is written. I want to overwrite the line.

For example, currently I have the below.

Structure x of y processed
Structure x of y processed
Structure x of y processed
Structure x of y processed

Eventually I fill up the buffer as I'm dealing with thousands of structure records.

Is there a method I can use that will just overwrite the last output line?

Answer 1

Using DBMS_OUTPUT means that SQL*Plus will display nothing until the entire PL/SQL block is complete and will then display all the data currently in the buffer. It is not, therefore, an appropriate way to provide an ongoing status.

On the other hand, Oracle does provide a package DBMS_APPLICATION_INFO that is specifically designed to help you monitor your running code. For example, you could do something like

CREATE PROCEDURE process_structures
AS
  <<other variable declarations>>

  rindex    BINARY_INTEGER;
  slno      BINARY_INTEGER;
  totalwork NUMBER := y; -- Total number of structures
  worksofar NUMBER := 0; -- Number of structures processed
BEGIN
  rindex := dbms_application_info.set_session_longops_nohint;

  FOR i IN (<<select structures to process>>)
  LOOP
    worksofar := worksofar + 1;
    dbms_application_info.set_session_longops(
        rindex      => rindex, 
        slno        => slno,
        op_name     => 'Processing of Molecular Structures', 
        sofar       => worksofar , 
        totalwork   => totalwork, 
        target_desc => 'Some description',
        units       => 'structures');
    <<process your structure with your existing code>>
  END LOOP;
END;

From a separate SQL*Plus session, you can then monitory progress by querying the V$SESSION_LONGOPS view

SELECT opname,
       target_desc,
       sofar,
       totalwork,
       units,
       elapsed_seconds,
       time_remaining
  FROM v$session_longops
 WHERE opname = 'Processing of Molecular Structures';

Answer 2

You may also send messages to a named pipe and have another process read the message from the pipe.

   procedure sendmessage(p_pipename varchar2
                        ,p_message  varchar2) is
      s number(15);
   begin
      begin
         sys.dbms_pipe.pack_message(p_message);
      exception
         when others then
            sys.dbms_pipe.reset_buffer;
      end;

      s := sys.dbms_pipe.send_message(p_pipename, 0);

      if s = 1
      then
         sys.dbms_pipe.purge(p_pipename);
      end if;
   end; 


   function receivemessage(p_pipename varchar2
                          ,p_timeout  integer) return varchar2 is
      n   number(15);
      chr varchar2(200);
   begin
      n := sys.dbms_pipe.receive_message(p_pipename, p_timeout);

      if n = 1
      then
         return null;
      end if;

      sys.dbms_pipe.unpack_message(chr);
      return(chr);
   end;