performnce tuning documentation

Need for performance tuning

In this world of SAP programming, ABAP is the universal language. In most of the projects, the focus is on getting a team of ABAP programmers as soon as possible, handing over the technical specifications to them and asking them to churn 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.

Use of selection criteria
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.
Not recommended
Select * from zflight.
Check : zflight-airln = ‘LF’ and zflight-fligh = ‘BW222’.
Endselect.
Recommended
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.
Use of aggregate functions
Use the already provided aggregate functions, instead of finding out the minimum/maximum values using ABAP code.
Not recommended
Maxnu = 0.
Select * from zflight where airln = ‘LF’ and cntry = ‘IN’.
Check zflight-fligh > maxnu.
Maxnu = zflight-fligh.
Endselect.

Recommended
Select max( fligh ) from zflight into maxnu 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).




Use of Views instead of base 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.
Not recommended
Select * from zcntry where cntry like ‘IN%’.
Select single * from zflight where cntry = zcntry-cntry and airln = ‘LF’.
Endselect.

Recommended
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.
Not recommended
Refresh: int_fligh.
Select * from zflight into int_fligh.
Append int_fligh. Clear int_fligh.
Endselect.
Recommended
Refresh: int_fligh.
Select * from zflight into table int_fligh.
Modifying a group of lines of an internal table
Use the variations of the modify command to speed up this kind of processing.
Not recommended
Loop at int_fligh.
If int_fligh-flag is initial.
Int_fligh-flag = ‘X’.
Endif.
Modify int_fligh.
Endloop.
Recommended
Int_fligh-flag = ‘X’.
Modify int_fligh transporting flag where flag is initial.
Use of binary search option
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.
Not Recommended
Read table int_fligh with key airln = ‘LF’.
Recommended
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.
Not Recommended
Loop at int_fligh1.
Append int_fligh1 to int_fligh2.
Endloop.
Recommended
Append lines of int_fligh1 to int_fligh2.


Using table buffering
Use of buffered tables is recommended to improve the performance considerably. The buffer is bypassed while using the following statements
1. Select distinct
2. Select … for update
3. Order by, group by, having clause
4. Joins


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






Use of 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
1. 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.
2. 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.
3. 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.
Not Recommended
Loop at int_cntry.
Select single * from zfligh into int_fligh
where cntry = int_cntry-cntry.
Append int_fligh.
Endloop.

Recommended
Select * from zfligh appending table int_fligh
For all entries in int_cntry
Where cntry = int_cntry-cntry.




Proper 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.
Proper use of 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.
Proper use of 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.



Use of ABAP Sort instead 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 Analysis
Following are the different tools provided by SAP for performance analysis of an ABAP object
1. 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.
2. 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.