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Use the GET RUN TIME command to help evaluate performance. It's hard to know whether that optimization technique REALLY helps unless you test it out. Using this tool can help you know what is effective, under what kinds of conditions. The GET RUN TIME has problems under multiple CPUs, so you should use it to test small pieces of your program, rather than the whole program.
Generally, try to reduce I/O first, then memory, then CPU activity. I/O operations that read/write to hard disk are always the most expensive operations. Memory, if not controlled, may have to be written to swap space on the hard disk, which therefore increases your I/O read/writes to disk. CPU activity can be reduced by careful program design, and by using commands such as SUM (SQL) and COLLECT (ABAP/4).
Avoid 'SELECT *', especially in tables that have a lot of fields. Use SELECT A B C INTO instead, so that fields are only read if they are used. This can make a very big difference.
Field-groups can be useful for multi-level sorting and displaying. However, they write their data to the system's paging space, rather than to memory (internal tables use memory). For this reason, field-groups are only appropriate for processing large lists (e.g. over 50,000 records). If you have large lists, you should work with the systems administrator to decide the maximum amount of RAM your program should use, and from that, calculate how much space your lists will use. Then you can decide whether to write the data to memory or swap space.
Use as many table keys as possible in the WHERE part of your select statements.
Whenever possible, design the program to access a relatively constant number of records (for instance, if you only access the transactions for one month, then there probably will be a reasonable range, like 1200-1800, for the number of transactions inputted within that month). Then use a SELECT A B C INTO TABLE ITAB statement.
Get a good idea of how many records you will be accessing. Log into your productive system, and use SE80 -> Dictionary Objects (press Edit), enter the table name you want to see, and press Display. Go To Utilities -> Table Contents to query the table contents and see the number of records. This is extremely useful in optimizing a program's memory allocation.
Try to make the user interface such that the program gradually unfolds more information to the user, rather than giving a huge list of information all at once to the user.
Declare your internal tables using OCCURS NUM_RECS, where NUM_RECS is the number of records you expect to be accessing. If the number of records exceeds NUM_RECS, the data will be kept in swap space (not memory).
Use SELECT A B C INTO TABLE ITAB whenever possible. This will read all of the records into the itab in one operation, rather than repeated operations that result from a SELECT A B C INTO ITAB... ENDSELECT statement. Make sure that ITAB is declared with OCCURS NUM_RECS, where NUM_RECS is the number of records you expect to access.
If the number of records you are reading is constantly growing, you may be able to break it into chunks of relatively constant size. For instance, if you have to read all records from 1991 to present, you can break it into quarters, and read all records one quarter at a time. This will reduce I/O operations. Test extensively with GET RUN TIME when using this method.
Know how to use the 'collect' command. It can be very efficient.
Use the SELECT SINGLE command whenever possible.
Many tables contain totals fields (such as monthly expense totals). Use these avoid wasting resources by calculating a total that has already been calculated and stored.
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. Information on the SAP R/3 ABAP/4 Development Workbench programming tools and its features can be found on the SAP Public Web-Server. --------------------------------------------------------------------------------- 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 Experience counts
--------------------------------------------------------------------------------- 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 (for more information, goto Transaction SE30 – Tips & Tricks) --------------------------------------------------------------------------------- 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') 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 eimproved 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 consumprion 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
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