SAP程序性能优化

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.