GRC
HR
SCM
CRM
BI


Article

 

How Plausibility Checks Detect Bottlenecks in ABAP Programming

by Axel Kurka | SAPinsider

January 1, 2001

by Axel Kurka, SAP SAPinsider - 2001 (Volume 2), January (Issue 1)
 

Despite the value of software reuse, reuse can sometimes produce performance problems, and often standard performance tests cannot unveil these issues completely. Plausibility checks, however, can help find performance bottlenecks, as in this example using the ABAP Runtime Analysis tool.

On my last summer vacation, I had an experience that was strikingly familiar - one that I think most software programmers will also recognize in their own projects. On this vacation, my family and I spent two days on Vancouver Island, Canada. Our hotel, with a strong British heritage, was praised for its famous afternoon tea, and I convinced my family to take part in this major tourist attraction.

     On the first day, we found that afternoon tea was "sold out" and learned that a "reservation at the dining reservation desk is mandatory." The next day, we approached the dining room - with our reservation - to find... a terribly long line. It took us 20 minutes to be seated, a delay that killed any enthusiasm we might have had. But if only guests with reservations are permitted, I wondered, why the delay?

     When we reached the head of the line, the reason was quite apparent: only a single host was seating the guests. While this procedure may have worked quite well with more staff, fewer tables, and fewer guests, it was now creating a bottleneck - and an absolutely avoidable one, at that.

Bottlenecks in the Tearoom - And In Your Applications

Why do I waste your time with my travel story? Because, as unlikely as it seems, it's a good analogy to performance problems in computer programs!

     Many programmers have experienced this phenomenon of software engineering: software components are often deployed under conditions they were not developed for. You can find this effect with both simple functions and complete packages.

     It's an undesired consequence of a highly valuable principle of software reuse: reuse of components can considerably improve the quality of a system - even if the components are constructed for a slightly different situation. On the other hand, it's the most important reason that the same software package works well in one condition and produces performance problems in another.

     Even worse, it's very unlikely that standard performance tests can unveil these issues completely. What can help, though, are simple plausibility checks.

     To encourage you to use plausibility checks to find performance bottlenecks, I'll give you an example prepared by Thomas Manzke, a key developer in SAP's ABAP department.

     This problem was originally detected by the SAP Performance Group, a unit that puts much effort in improving the performance of SAP software.

It's very unlikely that standard performance tests can unveil performance problems completely. What can help, though, are simple plausibility checks.

Detecting Application Bottlenecks for ABAP Software

If you need a gauge for time measurement in ABAP programs, you use ABAP Runtime Analysis. It enables programmers to find performance problems before deployment, and allows the system administrator to analyze bottlenecks during deployment of software written in ABAP. In the October 2000 issue of SAP Insider, I presented the ABAP Short Dump as an instrument that qualifies ABAP as "the Business Application Language," and with ABAP Runtime Analysis, I'll give you another helpful tool.

     ABAP Runtime Analysis consists of a recording component and an analysis component. Although it was available for ABAP early on, ABAP Runtime Analysis was completely revamped with Release 4.6, and now allows the user to record dramatically more data and to record the data of any executing process. To start recording, choose transaction SE30.

Use the Measurement frame to specify the object - program, function module, or transaction - and the session you are interested in. To record data of the current session, press the "Execute" button. ABAP Runtime then automatically executes the specified object and starts recording. If you use the "Back" button, recording of the session is terminated and the overview of the ABAP Runtime Analysis Evaluation appears. To "catch" a different session, press the "Enable/Disable" button.

In the Restrictions frame, you specify the variant that you want to use: "Default" or individually defined. You define a variant in order to describe how the recording is performed and what data is recorded.

To define the variant, you:

  1. Select the aggregation mode. (Note that the degree of aggregation influences the size of the trace file and the resolution of the analysis. In order to produce a hit list of only the most important performance consumers, use "Full" aggregation.)
  2. Restrict the size of the trace file.
  3. Restrict the recording time.
  4. Restrict recording to specific ABAP statements.
  5. Restrict recording to specific programs or procedural units.

Using the Performance file frame, you can analyze the actual trace file.

Testing an Application Using Plausibility Checks

The test candidate is ME21, a transaction used to create a purchase order. The test should determine whether the execution time of the transaction is growing linearly along with the number of order items - which would be plausible because there are no dependencies between the items. So we decided to record performance data for two purchase orders: one with 50 items and one with 495 items.

     It's crucial to understand that merely comparing the elapsed times of the two transactions would be misleading. Business transactions always include SQL statements, and the elapsed time of SQL statements is influenced by many factors, including net traffic, table buffers, etc. As a result, the elapsed times of two executions of a single SQL statement always differ. You can use the ABAP Runtime Analysis "Hit List" icon (on the overview window) to get more detailed information. The hit list is a presentation of the top "performance consumers" in transaction ME21: function modules, form routines, methods, and SQL statements. After sorting the hit lists of the 50-item order and the 495-item order according to net execution time, we are able to start our research.

     When investigating performance issues, it's always a good idea to start with only the biggest performance users, and then proceed to the lesser "performance hogs." (But be careful when deciding who's who - in a linearity check, even a 0.3-percent consumer may be using a large amount of execution time.)

     The first step is to find lines in the hit list of the 495-item order that are significantly more expensive (i.e., take the longest execution time) than those in the 50-item order. Again, SQL statements (OPEN, FETCH, etc.) must be checked in separate tests. This can easily be done by comparing the corresponding entries in the "Net (%)" (net percentage) column.

     Now the surprise: the ME_CHECK_ PRICING_RESULT function module requires 0.3 percent of the total execution time in the first purchase order, but takes 1.4 percent of the total time in the second one. Moreover, gross and net time are identical, which means within this function module there is no SQL, function call, or PERFORM statement. This is suspicious, even if its share in the complete elapsed time is relatively small.

     To display the ABAP source code of the function module, select the "Display source code" button.

     In our example, the culprit was found in the ABAP statement in Listing 1. The LOOP statement performs a linear search of the item number on the internal table T_KOMV. This table holds the pricing conditions of all items in the order. A single item may have no pricing conditions or thousands - the size of this table isn't really predictable. With most purchase orders, a linear search may work without any problems. But with 100,000 table entries, it produces a performance disaster (something like the afternoon tea in my travel story). A simple plausibility check executed with a professional tool helped to find a potential performance bottleneck! I hope that you now eagerly try out SE30.

LOOP AT t_komv WHERE kposn = i_ekpo-ebelp.
...
ENDLOOP.
Listing 1 "Bottleneck" ABAP Code

Solving the Performance Problem

So we've analyzed the problem, but what is the solution?

     Efficient access to an internal table can be established by hash or binary search. A binary search assumes that the internal table is sorted by the field KPOSN, a fact that is given in the example. Replacing the statement in Listing 1 with Listing 2 actually solves our problem.

READ TABLE t_komv WITH KEY kposn = i_ekpo-ebelp BINARY SEARCH.
IF sy-subrc = 0. 
  LOOP AT t_komv FROM sy-tabix.
    IF t_komv-kposn NE i_ekpo-ebelp. EXIT. ENDIF.
    ...
  ENDLOOP. 
ENDIF.
Listing 2 ABAP Code to Correct the Bottleneck

     Now, what if T_KOMV isn't sorted by KPOSN? Think about the SORTED TABLE construct - then visit the ABAP online documentation for more information.

SAP Online Resources

SAP
www.mysap.com

Business Intelligence
www.sap.com/solutions/bi

Business Information Warehouse
www.sap.com/bw
http://service.sap.com/bw

Knowledge Management
www.sap.com/km
http://service.sap.com/km

Strategic Enterprise Management
www.sap.com/sem
http://service.sap.com/sem

 

SAP C-Business Scenarios
www.sap.com/c-bs

SAP Plug-Ins
http://service.sap.com/
r3-plug-in

SAP Resources Supporting C-Business Scenarios

Application Link Enabling (ALE)
http://service.sap.com/ale

SAP Business Connector
http://service.sap.com/
connectors

Computing Center Management System (CCMS)
http://service.sap.com/
systemmanagement

Internet Adviser
http://service.sap.com/
internetadviser

SAP Internet Transaction Server (ITS)
http://service.sap.com/
sap-its

SAP Security
http://service.sap.com/
security

WebFlow
http://service.sap.com/
webflow

mySAP Workplace www.sap.com/solutions/
workplace

 


Axel Kurka is Product Manager of ABAP and GUI at SAP, where he has worked in several development departments. He can be reached at axel.kurka@sap.com.

An email has been sent to:






More from SAPinsider



COMMENTS

Please log in to post a comment.

No comments have been submitted on this article. Be the first to comment!


SAPinsider
FAQ