ABAP looping forever

Question

<b>Brief explanation of problem:</b>
I have a report that processes a lot of data.  The amount of data is dependent on what the user selects on the selection screen, but even for one entry in selection criteria, there could be thousands of records and millions of loops.
The problem, in the report, seems to be that when a user selects a range of entries (A* or A00 – DZZ), the program (scheduled in background) runs for a very long time.  Typically it the execution time is less than 30-40 seconds for one entry, but even for 30 entries, the report only averages about 1,000 seconds.
When the report is selecting a large amount of data, it seems the report just keeps on running, sometimes well over 100,000 seconds.  I’m not using any DO or WHILE loops, which can run infinitely, these are simply multiple nested (large) loops, up to 8 nested loops.  I have also monitored the memory usage of the background work process; it seems the memory levels-out after a certain point (about 500MB for large amount of data) and doesn’t increase or decrease.  I just cancel the report when it gets to that point and re-run it for smaller set of entries, and that works just fine.
<b>Now the questions:</b>
1) Can anyone diagnose the problem?  Or am I just canceling the report too early?
2) Is there a limit, when reached, the ABAP program goes in some sort of infinite loop?

Answer 1

Hi
There is not so much to add. It is obvious that some tuning measures should be taken. Some of the following will repeat the above recommendations. However let me write:
<b>1.</b> "BINARY SEARCH" addition may make great positive effect, however do not forget to sort your tables (The standard table must be sorted in ascending order by the specified search key).
<b>2.</b> Try giving your loop conditions with 'WHERE' statement instead of using 'CHECK'.
e.g.
LOOP AT gt_itab WHERE field_1 = 'A' .
ENDLOOP .
<u>is better than</u>
LOOP AT gt_itab .
CHECK gt_itab-field_1 = 'A' .
ENDLOOP .
<b>3.</b> If it is possible to specify keys, prefer using "READ TABLE...WITH KEY..." instead of "LOOP...ENDLOOP" to read single records.
<b>4.</b> Try using "WHILE...ENDWHILE" or "DO...ENDDO" if possible for looping. "WHILE...ENDWHILE" is better if you can prefer it.
<b>5.</b> Optimize your SELECT statements if any exists inside your loops.
__a. Prefer "SELECT SINGLE..." for reading single records and "SELECT...INTO TABLE..."(array fetch) to read multiple records.
__b. Try explicitly defining the fields you want to select. e.g. "SELECT field_1 field_2" is better than "SELECT * ".
__c. Eliminate redundant selection conditions.
__d. Generate secondary indices for the relevant tables if required.
__e. Hesitate from sophisticated selection conditions.
<b>6.</b> You can code some "WRITE" statements to trace the program execution. You can see the list output at debugging session by pressing the relevant button.
<b>7.</b> Use the "Runtime Analysis Tool" (SE30) to analyze your session for a reasonable set of data to see the relational execution time comparison between logical execution blocks of your program.
<b>8.</b> Try parallel processing. You can also consider exporting/importing generated lists.
Hope you can solve your problem...
*--Serdar
[email protected]