Algorithms in ABAP

Question

Hello folks,
I'm looking for material (books or anything) describing the developement of effective algorithms in ABAP, and the measurement of the performance of the used concepts. I'm thinking about the possibility to write my Bachelor Thesis about an SAP related topic, and so I've began to sift through the material available.
Your hints are pretty welcome.
Thanks & regards
Gerd

Answer 1

Hi,
Here are some ABAP code performance tips:
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 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 statement can not be used with a buffered table, so when using these statements the buffer will be bypassed. These statements are:
•     Select DISTINCT
•     ORDER BY / GROUP BY / HAVING clause
•     Any WHERE clause that contains a sub query or IS NULL expression
•     JOIN s
•     A SELECT... FOR UPDATE
If you wan t to explicitly bypass the buffer, 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 database server will usually be the bottleneck, so sometimes it is better to move the sort from the database 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 statement 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 database server sort it.
Avoid the 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 duplicate rows.
Sreedhar