What is the need of optimizing performance?

In SAP programming, ABAP is the language used. Most of the projects focuses on getting a team of ABAP programmers as soon as possible and handing over the technical specifications to them and asking them to make out the ABAP programs within the "given deadlines".

Often due to this pressure of schedules and deliveries, the main focus of making a efficient program takes a back seat. An efficient ABAP program is one which delivers the required output to the user in a finite time as per the complexity of the program, rather than hearing the comment "I put the program to run, have my lunch and come back to check the results".

Leaving aside the hyperbole, a performance optimized ABAP program saves the time of the end user, thus increasing the productivity of the user, and in turn keeping the user and the management happy.

This tutorial focuses on presenting various performance tuning tips and tricks to make the ABAP programs efficient in doing their work. This tutorial also assumes that the reader is well versed in all the concepts and syntax of ABAP programming.

Performance of a program is also often limited due to hardware restrictions, which is out of the scope of this article.

Correct Way For Selection

Instead of selecting all the data and doing the processing during the selection, it is advisable to restrict the data to the selection criteria itself, rather than filtering it out using the ABAP code.

Incorrect

Select * from zflight.

Check : zflight -airln = 'LF' and zflight-fligh = 'BW222'.

Endselect.

Correct Select * from zflight where airln = 'LF' and fligh = '222'.

Endselect.

One more point to be noted here is of the select *. Often this is a lazy coding practice. When a programmer gives select * even if one or two fields are to be selected, this can significantly slow the program and put unnecessary load on the entire system. When the application server sends this request to the database server, and the database server has to pass on the entire structure for each row back to the application server. This consumes both CPU and networking resources, especially for large structures.

Thus it is advisable to select only those fields that are needed, so that the database server passes only a small amount of data back.

Also it is advisable to avoid selecting the data fields into local variables as this also puts unnecessary load on the server. Instead attempt must be made to select the fields into an internal table.

How To use aggregate functions

Using the already provided aggregate functions, instead of finding out the minimum/maximum values using ABAP code.

Incorrect Maximum_numb = 0.

Select * from zflight where airln = 'LF' and cntry = 'IN'.

Check zflight -fligh > maximum_numb.

Maximum_numb = zflight -fligh.

Endselect.

Correct Select max( field ) from ztable into maximum_numb where airln = 'LF' and cntry = 'IN'.

The other aggregate functions that can be used are min (to find the minimum value), avg (to find the average of a Data interval), sum (to add up a data interval) and count (counting the lines in a data selection).

Using Views in place of tables

Many times ABAP programmers deal with base tables and nested selects. Instead it is always advisable to see whether there is any view provided by SAP on those base tables, so that the data can be filtered out directly, rather than specially coding for it.

Incorrect

Select * from zcntry where cntry like 'IN%'.

Select single * from zflight where cntry = zcntry-cntry and airln = 'LF'.

Endselect.

Correct

Select * from zcnfl where cntry like 'IN%' and airln = 'LF'.

Endselect.

Use of the into table clause of select statement

Instead of appending one record at a time into an internal table, it is advisable to select all the records in a single shot.

Incorrect

Refresh: int_fligh.

Select * from zflight into int_fligh.

Append int_fligh. Clear int_fligh.

Endselect.

Correct

Refresh: int_fligh.

Select * from zflight into table int_fligh.

Modify cluster of lines

Use the variations of the modify command to speed up this kind of processing.

Incorrect

Loop at int_fligh.

If int_fligh-flag is initial.

Int_fligh-flag = 'X'.

Endif.

Modify int_fligh.

Endloop.

Correct

Int_fligh-flag = 'X'.

Modify int_fligh transporting flag where flag is initial.

Binary Search

When a programmer uses the read command, the table is sequentially searched. This slows down the processing. Instead of this, use the binary search addition. The binary search algorithm helps faster search of a value in an internal table. It is advisable to sort the internal table before doing a binary search. Binary search repeatedly divides the search interval in half. If the value to be searched is less than the item in the middle of the interval, the search is narrowed to the lower half, otherwise the search is narrowed to the upper half.

Incorrect

Read table int_fligh with key airln = 'LF'.

Correct

Read table int_fligh with key airln = 'LF' binary search.

Appending 2 internal tables

Instead of using the normal loop-endloop approach for this kind of programming, use the variation of the append command. Care should be taken that the definition of both the internal tables should be identical.

Incorrect

Loop at int_fligh1.

Append int_fligh1 to int_fligh2.

Endloop.

Correct

Append lines of int_fligh1 to int_fligh2.

Table Buffering

Use of buffered tables is recommended to improve the performance considerably. The buffer is bypassed while using the following statements

Select distinct
Select ... for update
Order by, group by, having clause
Joins

Use the Bypass buffer addition to the select clause in order to explicitly bypass the buffer while selecting the data.

FOR ALL Entries

Outer join can be created using this addition to the where clause in a select statement. It speeds up the performance tremendously, but the cons of using this variation are listed below

Duplicates are automatically removed from the resulting data set. Hence care should be taken that the unique key of the detail line items should be given in the select statement.
If the table on which the For All Entries IN clause is based is empty, all rows are selected into the destination table. Hence it is advisable to check before-hand that the first table is not empty.
If the table on which the For All Entries IN clause is based is very large, the performance will go down instead of improving. Hence attempt should be made to keep the table size to a moderate level.

Incorrect

Loop at int_cntry.

Select single * from zfligh into int_fligh

where cntry = int_cntry-cntry.

Append int_fligh.

Endloop.

Correct

Select * from zfligh appending table int_fligh

For all entries in int_cntry

Where cntry = int_cntry-cntry.

Structure of Where Clause

When a base table has multiple indices, the where clause should be in the order of the index, either a primary or a secondary index.

To choose an index, the optimizer checks the field names specified in the where clause and then uses an index that has the same order of the fields. One more tip is that if a table begins with MANDT, while an index does not, there is a high possibility that the optimizer might not use that index.

In certain scenarios, it is advisable to check whether a new index can speed up the performance of a program. This will come handy in programs that access data from the finance tables.

Move Statement

Instead of using the move-corresponding clause it is advisable to use the move statement instead. Attempt should be made to move entire internal table headers in a single shot, rather than moving the fields one by one.

Inner Join

When multiple SAP tables are logically joined, it is always advisable to use inner join to read the data from them. This certainly reduces the load on the network.

Let us take an example of 2 tables, zairln and zflight. The table zairln has the field airln, which is the airline code and the field lnnam, which is the name of the airline. The table zflight has the field airln, the airline code and other fields which hold the details of the flights that an airline operates.

Since these 2 tables a re logically joined by the airln field, it is advisable to use the inner join.

Select a~airln a~lnnam b~fligh b~cntry into table int_airdet

From zairln as a inner join zflight as b on a~airln = b~airln.

In order to restrict the data as per the selection criteria, a where clause can be added to the above inner join.

Using ABAP Sort in place of Order By

The order by clause is executed on the database server, while the sort statement is executed on the application server. Thus instead of giving the order by in the select clause statement, it is better to collect the records in an internal table and then use the sort command to sort the resulting data set.

Tools provided for Performance

Following are the different tools provided by SAP for performance analysis of an ABAP object

Run time analysis transaction SE30

This transaction gives all the analysis of an ABAP program with respect to the database and the non-database processing.

SQL Trace transaction ST05

The trace list has many lines that are not related to the SELECT statement in the ABAP program. This is because the execution of any ABAP program requires additional administrative SQL calls. To restrict the list output, use the filter introducing the trace list.

The trace list contains different SQL statements simultaneously related to the one SELECT statement in the ABAP program. This is because the R/3 Database Interface - a sophisticated component of the R/3 Application Server - maps every Open SQL statement to one or a series of physical database calls and brings it to execution. This mapping, crucial to R/3s performance, depends on the particular call and database system. For example, the SELECT-ENDSELECT loop on the SPFLI table in our test program is mapped to a sequence PREPARE-OPEN-FETCH of physical calls in an Oracle environment.

The WHERE clause in the trace list's SQL statement is different from the WHERE clause in the ABAP statement. This is because in an R/3 system, a client is a self-contained unit with separate master records and its own set of table data (in commercial, organizational, and technical terms). With ABAP, every Open SQL statement automatically executes within the correct client environment. For this reason, a condition with the actual client code is added to every WHERE clause if a client field is a component of the searched table.

To see a statement's execution plan, just position the cursor on the PREPARE statement and choose Explain SQL. A detailed explanation of the execution plan depends on the database system in use.

User Exit	Customer Exit
User exit is implemented in the form of a Subroutine i.e. PERFORM xxx. Example: INCLUDE MVF5AFZZ à PERFORM userexit_save_document_prepare.	A customer exit can be implemented as: · Function exit · Screen Exit · Menu Exit · Field Exit Example: CALL Customer function ‘xxx’ INCLUDE xxx. You modify this include.
In case of a PERFORM, you have access to almost all the data. So you have better control, but more risk of making the system unstable.	You have access only to the importing, exporting, changing and tables parameter of the Function Module. So you have limited access to data.
User exit is considered a modification and not an enhancement.	A customer exit is considered an enhancement.
You need Access Key for User Exit.	You do not need access key.
Changes are lost in case of an upgrade.	Changes are upgrade compatible.
User exit is the earliest form of change option offered by SAP.	Customer exits came later and they overcome the shortcomings of User Exit.
No such thing is required here.	To activate a function exit, you need to create a project in SMOD and activate the project.

BAPI	RFC
Just as Google offers Image/Chart/Map APIs OR Facebook offers APIs for Comment/Like, SAP offers APIs in the form of BAPIs. BAPI is a library of function modules released by SAP to the public so that they can interface with SAP.	RFC is nothing but a remote enabled function module. So if there is a Function Module in SAP system 1 on server X , it can be called from a SAP system 2 residing on server Y.
There is a Business Object Associated with a BAPI. So a BAPI has an Interface, Key Field, Attributes, Methods, and Events.	No Business Object is associated with a RFC.
Outside world (JAVA, VB, .Net or any Non SAP system) can connect to SAP using a BAPI.	Non–SAP world cannot connect to SAP using RFC.
Error or Success messages are returned in a RETURN table.	RFC does not have a return table.

SAPSCRIPT	SMARTFORM
SAPSCRIPT is client dependent.	SMARTFORM is client independent.
SAPSCRIPT does not generate any Function module.	SMARTFORM generates a Function Module when activated.
Main Window is must.	You can create a SMARTFORM without a Main Window.
SAPSCRIPT can be converted to SMARTFORMS. Use Program SF_MIGRATE.	SMARTFORMS cannot be converted to SCRIPT.
Only one Page format is possible	Multiple page formats are possible.
Such thing is not possible in SCRIPT.	You can create multiple copies of a SMARTFORM using the Copies Window.
PROTECT … ENDPROTECT command is used for Page protection.	The Protect Checkbox can be ticked for Page Protection.

Session Method	Call Transaction
Session method id generally used when the data volume is huge.	Call transaction method is when the data volume is low
Session method is slow as compared to Call transaction.	Call Transaction method is relatively faster than Session method.
SAP Database is updated when you process the sessions. You need to process the sessions separately via SM35.	SAP Database is updated during the execution of the batch input program.
Errors are automatically handled during the processing of the batch input session.	Errors should be handled in the batch input program.

BAPI	BDC
BAPI is faster than BDC.	BDC is relatively slower than BAPI.
BAPI directly updates database.	BDC goes through all the screens as a normal user would do and hence it is slower.
No such processing options are available in BAPI.	Background and Foreground processing options are available for BDC.
BAPI would generally used for small data uploads.	BDCs would be preferred for large volumes of data upload since background processing option is available.
For processing errors, the Return Parameters for BAPI should be used.This parameter returns exception messages or success messages to the calling program.	Errors can be processed in SM35 for session method and in the batch input program for Call Transaction method.

SAP-ABAP useful codes

Sunday, 7 April 2013

SAP ABAP Interview Questions-usefull

SAP ABAP Interview Questions Part 1

SAP ABAP interview questions:

SAP ABAP Interview Questions Part 3 : Smartforms

BDC Interview Questions

ABAP interview questions on BDC:

ABAP Performance Standards

ABAP Performance Standards

What is the need of optimizing performance?

Correct Way For Selection

How To use aggregate functions

Using Views in place of tables

Use of the into table clause of select statement

Modify cluster of lines

Binary Search

Appending 2 internal tables

Table Buffering

FOR ALL Entries

Structure of Where Clause

Move Statement

Inner Join

Using ABAP Sort in place of Order By

Tools provided for Performance

Wednesday, 3 April 2013

WEBDynpro usefull Blogs

Macro	Subroutine
Macro can be called only in the program it is defined.	Subroutine can be called from other programs also.
Macro can have maximum 9 parameters.	Can have any number of parameters.
Macro can be called only after its definition.	This is not true for Subroutine.
A macro is defined inside: DEFINE … …. END-OF-DEFINITION.	Subroutine is defined inside: FORM ….. ….. ENDFORM.
Macro is used when same thing is to be done in a program a number of times.	Subroutine is used for modularization.

SAP Memory	ABAP Memory
When you are using the SET/GET Parameter ID command, you are using the SAP Memory.	When you are using the EXPORT IMPORT Statements, you are using the ABAP Memory.
SAP Memory is User Specific. What does this mean?àThe data stored in SAP memory can be accesses via any session from a terminal.	ABAP Memory is User and Transaction Specific.What does this mean?à The data stored in ABAP memory can be accessed only in one session. If you are creating another session, you cannot use ABAP memory.

Description	Result (Y, N or N/A)	Comments
Run Extended syntax checks with character literals checkbox switched on & Code Inspector to rectify all relevant errors and warning (e.g. Use the results of the above checks to remove all variables/constants etc that are declared but are not used)
Transaction SE30 (ABAP Runtime Analysis) must be checked to measure/compare program performance/runtime if program has multiple inefficient databases selects or complicated internal table operations
Use transaction ST05 (SQL Trace) to see what indices your database accesses are using. Check these indices against your “where” clause to assure they are significant. Check other indices for this table and where you have to change your “where” clause to use it. Create new indices if necessary, but do not forget to check the impact by consulting onsite coordinator.
TYPE (data element) command is used while declaring the fields whenever feasible instead of LIKE. Remember not always the data element name matches with the table field name
Internal Table is defined with “TYPE STANDARD TABLE OF” & Work-Areas is used instead of header lines
Global variables are minimized by declaring local variables or by passing variables through parameters & arguments while creating internal subroutine(s)
In SELECT statement, only the required fields are selected in the same order as they reside on the database table/structure/view
For selecting single row from a database table, “SELECT UP to 1 Rows” is used. “Select Single” is used only when full primary key combination is known
No SELECT * is used
Use “SELECT INTO TABLE” rather than “SELECT INTO CORRESPONDING FIELDS OF TABLE”
Always specify as many primary keys as possible in WHERE clause to make the Select efficient
Always select into an internal table, except when the table will be very large (i.e., when the internal table will be greater than 500,000 records). Use “Up to N Rows” when the number of records needed is known
Select statement within a GET event is not used
Wild cards like ‘A%’ is avoided as much as possible
Nested Select is not used instead “Inner Join” and/or “For all Entries” is used. “For all Entries” is to be used over “Loop at ITAB / Select / ENDLOOP” (FOR ALL ENTRIES retrieves a unique result set so ensure you retrieve the full key from the database)
When creating joins over database tables there should be an index at least on the inner table for the fields in the join condition else use “ FOR ALL ENTRIES” select statement
Usage of JOIN is limited to a maximum of 2 i.e. not more than 3 database tables are joined at one time
CHECK that the internal table used in FOR ALL ENTRIES is NOT empty as this will retrieve all entries from the table
Delete adjacent duplicate entries from internal table before selection from database table using “ FOR ALL ENTRIES” statement
For copying internal tables use ‘=’ operator instead of Looping & Appending
SORT inside a LOOP is not used
Sort internal table by fields in the correct order, which are used in a READ TABLE statement using BINARY SEARCH. If the order of sorting is invalid the BINARY SEARCH will never work
For large internal tables where only some rows are to be processed, use SORT and then the READ TABLE command is used to set index to first relevant row before looping from that index. Use CHECK or IF…EXIT…ENDIF as appropriate to exit from the loop
Sort fields and Sort Order on the SORT statement should be mentioned explicitly (e.g. SORT ITAB BY FLD1 FLD2 ASCENDING)
Hashed table is used for processing large amount of data (provided that you access single records only, and all with a fully specified key)
DELETE or SORT is not used on a hashed table since it increases memory consumption
Sorted table is used for range accesses involving table key or index accesses
Fields specified in the WHERE condition with the critical operators NOT and <> (negative SQL statements) cannot be used for a search using database indexes. Whenever possible formulate SQL statements positively
When coding IF or CASE, testing conditions are nested so that the most frequently true conditions are processed first. Also CASE is used instead of IF when testing multiple fields “equal to” something
LOOP AT ITAB INTO WORKAREA WHERE K = ‘XXX’ should be used instead of LOOP AT ITAB INTO WORKAREA / CHECK ITAB-K = ‘XXX’.Also READ TABLE INTO WORKAREA should be used instead of only READ TABLE.
After the APPEND statement inside a loop, the work area that has been appended is cleared
Internal tables, Work areas & Global Variables are freed when no longer needed (e.g. using the FREE / REFRESH command), especially when the tables are large or the program is a batch program
Do not delete the records of internal table inside the Loop – End loop. Do not use: LOOP AT ITAB WHERE EQUNR = ‘00001011’. DELETE ITAB. ENDLOOP. Use: DELETE ITAB WHERE EQUNR = ‘00001011’.
Use the MODIFY ITAB ... TRANSPORTING f1 f2 ... for single line, and MODIFY ITAB ... TRANSPORTING f1 f2 ... WHERE condition for a set of line, to accelerate the updating of internal table
If possible, Update/Insert statement is used instead of Modify
Is the following steps ensured during database updates? Lock data to be edited Read current data from the database Process data and write it to the database Release the locks set at the beginning
Try to avoid logical databases. If your program uses a logical database, but does not require all fields belonging to a certain GET event, always use the FIELDS addition to reduce the amount of data selected by the logical database
Avoid the aggregate (Count, Max, Min) functions in the database selection
Use Parallel Cursor methods for nested loop into the internal tables if second internal table contains considerable number of records
In Smartform/ Sapscript do not make redundant data retrieval where data is available in interface