Performance tuning for Data Selection Statement SAP ABAP INTERVIEW Questions

For all entries

The for all entries creates a where clause, where all the entries in the driver table are combined with OR. If the number of
entries in the driver table is larger than rsdb/max_blocking_factor, several similar SQL statements are executed to limit the
length of the WHERE clause.

The plus

• Large amount of data
• Mixing processing and reading of data
• Fast internal reprocessing of data
• Fast

The Minus

• Difficult to program/understand
• Memory could be critical (use FREE or PACKAGE size)

Some steps that might make FOR ALL ENTRIES more efficient:

• Removing duplicates from the the driver table
• Sorting the driver table
  If possible, convert the data in the driver table to ranges so a BETWEEN statement is used instead of and OR statement:
  FOR ALL ENTRIES IN i_tab
  WHERE mykey >= i_tab-low and
  mykey <= i_tab-high.

Nested selects

The plus:

• Small amount of data
• Mixing processing and reading of data
• Easy to code - and understand

The minus:

• Large amount of data
• when mixed processing isn’t needed
• Performance killer no. 1

Select using JOINS

The plus

• Very large amount of data
• Similar to Nested selects - when the accesses are planned by the programmer
• In some cases the fastest
• Not so memory critical

The minus

• Very difficult to program/understand
• Mixing processing and reading of data not possible

Use the selection criteria

SELECT * FROM SBOOK.                
CHECK: SBOOK-CARRID = 'LH' AND    
               SBOOK-CONNID = '0400'.     
ENDSELECT.                              

SELECT * FROM SBOOK                  
WHERE CARRID = 'LH' AND            
     CONNID = '0400'.             
ENDSELECT.                               

Use the aggregated functions

C4A = '000'.           
SELECT * FROM T100     
WHERE SPRSL = 'D' AND
     ARBGB = '00'.  
CHECK: T100-MSGNR > C4A.
C4A = T100-MSGNR.    
ENDSELECT.             

SELECT MAX( MSGNR ) FROM T100 INTO C4A
WHERE SPRSL = 'D' AND             
    ARBGB = '00'.                   

Select with view

SELECT * FROM DD01L                 
WHERE DOMNAME LIKE 'CHAR%'        
     AND AS4LOCAL = 'A'.         
SELECT SINGLE * FROM DD01T        
 WHERE   DOMNAME    = DD01L-DOMNAME
     AND AS4LOCAL   = 'A'        
     AND AS4VERS    = DD01L-AS4VERS
     AND DDLANGUAGE = SY-LANGU.  
ENDSELECT.                          

SELECT * FROM DD01V                 
WHERE DOMNAME LIKE 'CHAR%'        
    AND DDLANGUAGE = SY-LANGU.  
ENDSELECT.                              

Select with index support

SELECT * FROM T100         
WHERE     ARBGB = '00'   
    AND MSGNR = '999'. 
ENDSELECT.                 

SELECT * FROM T002.          
SELECT * FROM T100         
 WHERE     SPRSL = T002-SPRAS
       AND ARBGB = '00'   
       AND MSGNR = '999'. 
ENDSELECT.                 
ENDSELECT.                       

Select … Into table

REFRESH X006.              
SELECT * FROM T006 INTO X006.
APPEND X006.             
ENDSELECT

SELECT * FROM T006 INTO TABLE X006.

Select with selection list

SELECT * FROM DD01L           
WHERE DOMNAME LIKE 'CHAR%'  
     AND AS4LOCAL = 'A'.   
ENDSELECT

SELECT DOMNAME FROM DD01L 
INTO DD01L-DOMNAME      
WHERE DOMNAME LIKE 'CHAR%'
    AND AS4LOCAL = 'A'.
ENDSELECT

Key access to multiple lines

LOOP AT TAB.       
CHECK TAB-K = KVAL.
" ...            
ENDLOOP.           

LOOP AT TAB WHERE K = KVAL.  
" ...                      
ENDLOOP.                         

Copying internal tables

REFRESH TAB_DEST.           
LOOP AT TAB_SRC INTO TAB_DEST.
APPEND TAB_DEST.          
ENDLOOP.                    

TAB_DEST[] = TAB_SRC[].

Modifying a set of lines

LOOP AT TAB.          
IF TAB-FLAG IS INITIAL.
 TAB-FLAG = 'X'.   
ENDIF.              
MODIFY TAB.         
ENDLOOP.              

TAB-FLAG = 'X'.               
MODIFY TAB TRANSPORTING FLAG  
        WHERE FLAG IS INITIAL. 

Deleting a sequence of lines

DO 101 TIMES.            
DELETE TAB_DEST INDEX 450.
ENDDO.                   

DELETE TAB_DEST FROM 450 TO 550.

Linear search vs. binary

READ TABLE TAB WITH KEY K = 'X'.

READ TABLE TAB WITH KEY K = 'X' BINARY SEARCH.

Comparison of internal tables

DESCRIBE TABLE: TAB1 LINES L1,   
             TAB2 LINES L2.   
                              
IF L1 <> L2.                     
TAB_DIFFERENT = 'X'.           
ELSE.                            
TAB_DIFFERENT = SPACE.         
LOOP AT TAB1.                  
 READ TABLE TAB2 INDEX SY-TABIX.
 IF TAB1 <> TAB2.             
   TAB_DIFFERENT = 'X'. EXIT. 
 ENDIF.                       
ENDLOOP.                       
ENDIF.                           
                              
IF TAB_DIFFERENT = SPACE.        
" ...                          
ENDIF.                           

IF TAB1[] = TAB2[].
" ...           
ENDIF.                

Modify selected components

LOOP AT TAB.        
TAB-DATE = SY-DATUM.
MODIFY TAB.       
ENDLOOP.            

WA-DATE = SY-DATUM.                 
LOOP AT TAB.                        
MODIFY TAB FROM WA TRANSPORTING DATE.
ENDLOOP.                                

Appending two internal tables

LOOP AT TAB_SRC.           
APPEND TAB_SRC TO TAB_DEST.
ENDLOOP

APPEND LINES OF TAB_SRC TO TAB_DEST.

Deleting a set of lines

LOOP AT TAB_DEST WHERE K = KVAL.
DELETE TAB_DEST.            
ENDLOOP

DELETE TAB_DEST WHERE K = KVAL.

Tools available in SAP to pin-point a performance problem

The runtime analysis (SE30)

SQL Trace (ST05)

Tips and Tricks tool 

The performance database

Optimizing the load of the database

Using table buffering

Using buffered tables improves the performance considerably. Note that in some cases a stament can not be used with a buffered table, so when using these staments the buffer will be bypassed. These staments are:

• Select DISTINCT
• ORDER BY / GROUP BY / HAVING clause
• Any WHERE clasuse that contains a subquery or IS NULL expression
• JOIN s
• A SELECT... FOR UPDATE

If you wnat to explicitly bypass the bufer, use the BYPASS BUFFER addition to the SELECT clause.

Use the ABAP SORT Clause Instead of ORDER BY

The ORDER BY clause is executed on the database server while the ABAP SORT statement is executed on the application server. The datbase server will usually be the bottleneck, so sometimes it is better to move thje sort from the datsbase server to the application server.

If you are not sorting by the primary key ( E.g. using the ORDER BY PRIMARY key statement) but are sorting by another key, it could be better to use the ABAP SORT stament to sort the data in an internal table. Note however that for very large result sets it might not be a feasible solution and you would want to let the datbase server sort it.

Avoid ther SELECT DISTINCT Statement

As with the ORDER BY clause it could be better to avoid using SELECT DISTINCT, if some of the fields are not part of an index. Instead use ABAP SORT + DELETE ADJACENT DUPLICATES on an internal table, to delete duplciate rows.