Performance tuning for Data Selection Statement

Transfer form http://www.sap-img.com/abap/performance-tuning-for-data-selection-statement.htm

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.