Parallel Cursor Vs. Nested Loop

Nested Loops – This is one of the fear factors for all the ABAP developers as this consumes lot of program execution time. If the number of entries in the internal tables is huge, then the situation would be too worse. The solution for this is to use parallel cursor method whenever there is a need for Nested Loop.
  
Sample program to compare the Parallel Cursor Vs. Nested Loop:


*&---------------------------------------------------------------------*
*& Report  ZPARALLEL_CURSOR_Vs_NESTED LOOP
*&
*&---------------------------------------------------------------------*
*&
*&
*&---------------------------------------------------------------------*

REPORT  ZPARALLEL_CURSOR.

TYPES: ty_t_vbak TYPE STANDARD TABLE OF vbak.
DATA: it_vbak TYPE ty_t_vbak .
*
TYPES: ty_t_vbap TYPE STANDARD TABLE OF vbap.
DATA: it_vbap TYPE ty_t_vbap.
*
FIELD-SYMBOLS: <lfs_vbak> LIKE LINE OF it_vbak,
               <lfs_vbap> LIKE LINE OF it_vbap.
*
* necessary data selection
SELECT * FROM vbak
  INTO TABLE it_vbak
  UP TO 1000 ROWS.
CHECK it_vbak IS NOT INITIAL.
SELECT * FROM vbap
  INTO TABLE it_vbap
  FOR ALL ENTRIES IN it_vbak
  WHERE vbeln = it_vbak-vbeln.
*
DATA: lv_start_time TYPE timestampl,
      lv_end_time   TYPE timestampl,
      lv_diff       TYPE timestampl.
DATA: lv_tabix TYPE i.
*
*...... Normal Nested Loop .................................
* Get the Start Time
GET TIME STAMP FIELD lv_start_time.
*
* Nested Loop
LOOP AT it_vbak ASSIGNING <lfs_vbak>.
  LOOP AT it_vbap ASSIGNING <lfs_vbap>
                  WHERE vbeln = <lfs_vbak>-vbeln.
  ENDLOOP.
ENDLOOP.
*
* Get the end time
GET TIME STAMP FIELD lv_end_time.
*
* Actual time Spent:
lv_diff = lv_end_time - lv_start_time.
WRITE: /(50) 'Time Spent on Nested Loop', lv_diff.
*
CLEAR: lv_start_time, lv_end_time, lv_diff.
*
*....... Parallel Cursor with Nested Loop .......................
* Get the Start Time
GET TIME STAMP FIELD lv_start_time.
*
* Starting the Parallel Cursor
SORT: it_vbak BY vbeln,
      it_vbap BY vbeln.
LOOP AT it_vbak ASSIGNING <lfs_vbak>.
*
* Read the second internal table with BINARY SEARCH
  READ TABLE it_vbap TRANSPORTING NO FIELDS
       WITH KEY vbeln = <lfs_vbak>-vbeln
       BINARY SEARCH.
* Get the TABIX number
  lv_tabix = sy-tabix.
* Start the LOOP from the first accessed record in
* previous READ i.e. LV_TABIX
  LOOP AT it_vbap FROM lv_tabix ASSIGNING <lfs_vbap> .
*
*   End the LOOP, when there is no more record with similar key
    IF <lfs_vbap>-vbeln <> <lfs_vbak>-vbeln.
      EXIT.
    ENDIF.
*   Rest of the logic would go from here...
*
  ENDLOOP.
*
ENDLOOP.
*
* Get the end time
GET TIME STAMP FIELD lv_end_time.
*
* Actual time Spent:
lv_diff = lv_end_time - lv_start_time.
WRITE: /(50) 'Time Spend on Parallel Cursor Nested loops:', lv_diff.

Analysis report: Runtime in microseconds: