EFFECTIVE CODING IN ABAP 1

SAP R/3 : ABAP/4 Development Code Efficiency Guidelines


ABAP/4 (Advanced Business Application Programming 4GL) language is an "event-driven", "top-down", well-structured and powerful programming language. The ABAP/4 processor controls the execution of an event. Because the ABAP/4 language incorporates many "event" keywords and these keywords need not be in any specific order in the code, it is wise to implement in-house ABAP/4 coding standards.


SAP-recommended customer-specific ABAP/4 development guidelines can be found in the SAP-documentation. This page contains some general guidelines for efficient ABAP/4 Program Development that should be considered to improve the systems performance on the following areas:-


• Physical I/O - data must be read from and written into I/O devices. This can be a potential bottle neck. A well configured system always runs 'I/O-bound' - the performance of the I/O dictates the overall performance.


• Memory consumption of the database resources eg. buffers, etc.
• CPU consumption on the database and application servers
• Network communication - not critical for little data volumes, becomes a bottle neck when large volumes are transferred.


Policies and procedures can also be put into place so that every SAP-customer development object is thoroughly reviewed (quality – program correctness as well as code-efficiency) prior to promoting the object to the SAP-production system.

CLASSIC GOOD 4GL PROGRAMMING CODE-PRACTICES GUIDELINES


Avoid dead-code
Remove unnecessary code and redundant processing
Spend time documenting and adopt good change control practices
Spend adequate time anayzing business requirements, process flows, data-structures and data-model

Quality assurance is key: plan and execute a good test plan and testing methodology


SELECT * FROM TABLE
CHECK: CONDITION
ENDSELECT
vs.


SELECT * FROM TABLE
WHERE CONDITION
ENDSELECT



In order to keep the amount of data which is relevant to the query the hit set small, avoid using SELECT+CHECK statements wherever possible. As a general rule of thumb, always specify all known conditions in the WHERE clause (if possible). If there is no WHERE clause the DBMS has no chance to make optimizations.

Always specify your conditions in the Where-clause instead of checking them yourself with check-statements. The database system can also potentially make use a database index (if possible) for greater efficiency resulting in less load on the database server and considerably less load on the network traffic as well.


Also, it is important to use EQ (=) in the WHERE clause wherever possible, and analyze the SQL-statement for the optimum path the database optimizer will utilize via SQL-trace when necessary.


Also, ensure careful usage of "OR", "NOT" and value range tables (INTTAB) that are used inappropriately in Open SQL statements.



SELECT *
vs.


SELECT SINGLE *

If you are interested in exactly one row of a database table or view, use the SELECT SINGLE statement instead of a SELECT * statement. SELECT SINGLE requires one communication with the database system whereas SELECT * requires two.



SELECT * FROM TABLE INTO INT-TAB
APPEND INT-TAB
ENDSELECT
vs.


SELECT * FROM TABLE INTO TABLE INT-TAB

It is usually faster to use the INTO TABLE version of a SELECT statement than to use APPEND statements



SELECT ... WHERE + CHECK
vs.


SELECT using aggregate function

If you want to find the maximum, minimum, sum and average value or the count of a database column, use a select list with aggregate functions instead of computing the aggregates within the program. The RDBMS is responsible for aggregated computations instead of transferring large amount of data to the application. Overall Network, Application-server and Database load is also considerably less.



SELECT INTO TABLE INT-TAB + LOOP AT T
…………
SELECT * FROM TABLE INTO TABLE INT-TAB.
LOOP AT INT-TAB.
ENDLOOP.

vs.


SELECT * FROM TABLE
……….
ENDSELECT


If you process your data only once, use a SELECT-ENDSELECT loop instead of collecting data in an internal table with SELECT ... INTO TABLE. Internal table handling takes up much more space



Nested SELECT statements:
SELECT * FROM TABLE-A
SELECT * FROM TABLE-B
……..
ENDSELECT.
ENDSELECT
vs.


Select with view
SELECT * FROM VIEW
ENDSELECT

To process a join, use a view wherever possible instead of nested SELECT statements.


Using nested selects is a technique with low performance. The inner select statement is executed several times which might be an overhead. In addition, fewer data must be transferred if another technique would be used eg. join implemented as a view in ABAP/4 Repository.


• SELECT ... FORM ALL ENTRIES
• Explicit cursor handling


Nested select:
SELECT * FROM pers WHERE condition.
SELECT * FROM persproj WHERE person = pers-persnr.
... process ...
ENDSELECT.
ENDSELECT.

vs.


SELECT persnr FROM pers INTO TABLE ipers WHERE cond. ……….
SELECT * FROM persproj FOR ALL ENTRIES IN ipers
WHERE person = ipers-persnr
………... process .……………
ENDSELECT.


In the lower version the new Open SQL statement FOR ALL ENTRIES is used. Prior to the call, all interesting records from 'pers' are read into an internal table. The second SELECT statement results in a call looking like this (ipers containing: P01, P02, P03):

(SELECT * FROM persproj WHERE person = 'P01')
UNION
(SELECT * FROM persproj WHERE person = 'P02')
UNION
(SELECT * FROM persproj WHERE person = 'P03')



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EFFECTIVE CODING IN ABAP PART 2

EFFECTIVE CODING IN ABAP 2

In case of large statements, the R/3's database interface divides the statement into several parts and recombines the resulting set to one. The advantage here is that the number of transfers is minimized and there is minimal restrictions due to the statement size (compare with range tables).


SELECT * FROM TABLE
vs.

SELECT column(s) FROM TABLE


Use a select list or a view instead of SELECT *, if you are only interested in specific columns of the table. If only certain fields are needed then only those fields should be read from the database. Similarly, the number of columns can also be restricted by using a view defined in ABAP/4 Dictionary. Overall database and network load is considerably less.

SELECT without table buffering support
vs.

SELECT with table buffering support

For all frequently used, read-only(few updates) tables, do attempt to use SAP-buffering for improved
performance response times. This would reduce the overall Database activity and Network traffic.


Single-line inserts
LOOP AT INT-TAB
INSERT INTO TABLE VALUES INT-TAB
ENDLOOP
vs.

Array inserts

Whenever possible, use array operations instead of single-row operations to modify the database tables
Frequent communication between the application program and database system produces considerable overhead


Single-line updates
SELECT * FROM TABLE
COLUMN-UPDATE STATEMENT
UPDATE TABLE
ENDSELECT

vs.


Column updates
UPDATE TABLE SET COLUMN-UPDATE STATEMENT


Wherever possible, use column updates instead of single row updates to update your database tables


DO....ENDDO loop with Field-Symbol
vs.


Using CA operator


Use the special operators CO, CA, CS instead of programming the operations yourself
If ABAP/4 statements are executed per character on long strings, CPU consumption can rise substantially



Use of a CONCATENATE function module
vs.

Use of a CONCATENATE statement

Some function modules for string manipulation have become obsolete, and should be replaced by ABAP statements or functions


STRING_CONCATENATE... --- CONCATENATE
STRING_SPLIT... --- SPLIT
STRING_LENGTH... --- strlen()
STRING_CENTER... --- WRITE..TO. ..CENTERED
STRING_MOVE_RIGHT --- WRITE...TO...RIGHT-JUSTIFIED





Moving with offset
vs.


Use of the CONCATENATE statement

Use the CONCATENATE statement instead of programming a string concatenation of your own


Use of SEARCH and MOVE with offset

vs.


Use of SPLIT statement


Use the SPLIT statement instead of programming a string split yourself



Shifting by SY-FDPOS places
vs

Using SHIFT...LEFT DELETING LEADING...


If you want ot delete the leading spaces in a string use the ABAP/4 statements SHIFT...LEFT DELETING LEADING... Other constructions (with CN and SHIFT... BY SY-FDPOS PLACES, with CONDENSE if possible, with CN and ASSIGN CLA+SY-FDPOS(LEN) ...) are not as fast


Get a check-sum with field length
vs

Get a check-sum with strlen ()

Use the strlen () function to restrict the DO loop to the relevant part of the field, eg. when determinating a check-sum


Quick Note on Design of secondary database indexes

First it must be stated that table design is a more logical work while index design is rather technical. In table design it might make sense to place certain fields (client, company code, ...) in the beginning. In index design, this is not advisable. Very important for an index is that it contains very selective fields in the beginning. Those are fields like object numbers. Not selective are client, company code, ...


• Indexes should be small (few fields). The Database optimizer can combine two or more indexes to execute a query.


• Indexes of one table should be disjoint (have few common fields), in order not to confuse the optimizer which index to use.

Note that each index slows the inserts into the table down. Updates are only slowed down if indexed fields are updated. In general, heavy inserted tables should have only few indexes while heavy selected tables might have more.


Quick Note on Design of logical databases

Using logical databases is a good method to write reports. Logical databases can be optimized centrally. But ensure that the structure of the logical database fits well to your report. Otherwise the effect can be the opposite.


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EFFECTIVE CODING IN ABAP PART 1