What are the Optimization Techniques?

Question

What are the Optimization Techniques? Can any one send the one sample program which is having Good Optimization Techniques.
Phani

Answer 1

Hi phani kumarDurusoju  ,
ABAP/4 programs can take a very long time to execute, and can make other processes have to wait before executing. Here are
some tips to speed up your programs and reduce the load your programs put on the system:
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. See the Fieldgroups ABAP example.
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.
These r good websites which wil help u :
Performance tuning
http://www.sapbrainsonline.com/ARTICLES/TECHNICAL/optimization/optimization.html
http://www.geocities.com/SiliconValley/Grid/4858/sap/ABAPCode/Optimize.htm
http://www.abapmaster.com/cgi-bin/SAP-ABAP-performance-tuning.cgi
http://abapcode.blogspot.com/2007/05/abap-performance-factor.html
cheers!
gyanaraj
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