For all entries
The for all entriescreates a where clause, where all the entries in the driver table are combinedwith OR. If the number of entries in the driver table is larger than rsdb/max_blocking_factor,several similar SQL statements are executed to limit the length of the WHERE clause.
The plus
Large amount ofdata
Mixing processingand reading of data
Fast internalreprocessing of data
Fast
The Minus
Difficult toprogram/understand
Memory could becritical (use FREE or PACKAGE size)
Some steps that mightmake FOR ALL ENTRIES more efficient:
Removing duplicatesfrom the the driver table
Sorting the drivertable
Code:
If possible, convert the data in the driver table to ranges so a BETWEEN statement is used instead of and OR statement:
FOR ALL ENTRIES IN i_tab
WHERE mykey >= i_tab-low
AND mykey <= i_tab-high.
Nested selects
The plus:
Small amount ofdata
Mixing processingand reading of data
Easy to code - andunderstand
The minus:
Large amount ofdata
when mixedprocessing isn't needed
Performance killer no. 1
Select using JOINS
The plus
Very large amountof data
Similar to Nestedselects - when the accesses are planned by the programmer
In some cases thefastest
Not so memorycritical
The minus
Very difficult toprogram/understand
Mixing processing and reading of data not possible
Use the selection criteria
Code:
SELECT * FROM SBOOK.
CHECK: SBOOK-CARRID=LH' AND
SBOOK-CONNID=0400'.
ENDSELECT.
Code:
SELECT * FROM SBOOK
WHERE CARRID=LH' AND
CONNID=0400'.
ENDSELECT.
Use the aggregated functions
Code:
C4A=000'.
SELECT * FROM T100
WHERE SPRSL=D' AND
ARBGB=00'.
CHECK: T100-MSGNR > C4A.
C4A=T100-MSGNR.
ENDSELECT.
SELECT MAX( MSGNR ) FROM T100 INTO C4A
WHERE SPRSL=D' AND
ARBGB=00'.
Select with view
Code:
SELECT * FROM DD01L
WHERE DOMNAME LIKE 'CHAR%'
AND AS4LOCAL=A'.
SELECT SINGLE * FROM DD01T
WHERE DOMNAME =DD01L-DOMNAME
AND AS4LOCAL =A'
AND AS4VERS =DD01L-AS4VERS
AND DDLANGUAGE=SY-LANGU.
ENDSELECT.
SELECT * FROM DD01V
WHERE DOMNAME LIKE 'CHAR%'
AND DDLANGUAGE=SY-LANGU.
ENDSELECT.
Select with index support
Code:
SELECT * FROM T100
WHERE ARBGB=00'
AND MSGNR=999'.
ENDSELECT.
SELECT * FROM T002.
SELECT * FROM T100
WHERE SPRSL=T002-SPRAS
AND ARBGB=00'
AND MSGNR=999'.
ENDSELECT.
ENDSELECT.
Select : Into table
Code:
REFRESH X006.
SELECT * FROM T006 INTO X006.
APPEND X006.
ENDSELECT
SELECT * FROM T006 INTO TABLE X006.
Select with selection list
Code:
SELECT * FROM DD01L
WHERE DOMNAME LIKE 'CHAR%'
AND AS4LOCAL=A'.
ENDSELECT
SELECT DOMNAME FROM DD01L
INTO DD01L-DOMNAME
WHERE DOMNAME LIKE 'CHAR%'
AND AS4LOCAL=A'.
ENDSELECT
Key access to multiple lines
Code:
LOOP AT TAB.
CHECK TAB-K=KVAL.
" ...
ENDLOOP.
LOOP AT TAB WHERE K=KVAL.
" ...
ENDLOOP.
Copying internal tables
Code:
REFRESH TAB_DEST.
LOOP AT TAB_SRC INTO TAB_DEST.
APPEND TAB_DEST.
ENDLOOP.
TAB_DEST[]=TAB_SRC[].
Modifying a set of lines
Code:
LOOP AT TAB.
IF TAB-FLAG IS INITIAL.
TAB-FLAG=X'.
ENDIF.
MODIFY TAB.
ENDLOOP.
TAB-FLAG=X'.
MODIFY TAB TRANSPORTING FLAG
WHERE FLAG IS INITIAL.
Deleting a sequence of lines
Code:
DO 101 TIMES.
DELETE TAB_DEST INDEX 450.
ENDDO.
DELETE TAB_DEST FROM 450 TO 550.
Linear search vs. binary
Code:
READ TABLE TAB WITH KEY K=X'.
READ TABLE TAB WITH KEY K=X' BINARY SEARCH.
Comparison of internal tables
Code:
DESCRIBE TABLE: TAB1 LINES L1,
TAB2 LINES L2.
IF L1 <> L2.
TAB_DIFFERENT=X'.
ELSE.
TAB_DIFFERENT=SPACE.
LOOP AT TAB1.
READ TABLE TAB2 INDEX SY-TABIX.
IF TAB1 <> TAB2.
TAB_DIFFERENT=X'. EXIT.
ENDIF.
ENDLOOP.
ENDIF.
IF TAB_DIFFERENT=SPACE.
" ...
ENDIF.
IF TAB1[]=TAB2[].
" ...
ENDIF.
Modify selected components
Code:
LOOP AT TAB.
TAB-DATE=SY-DATUM.
MODIFY TAB.
ENDLOOP.
WA-DATE=SY-DATUM.
LOOP AT TAB.
MODIFY TAB FROM WA TRANSPORTING DATE.
ENDLOOP.
Appending two internal tables
Code:
LOOP AT TAB_SRC.
APPEND TAB_SRC TO TAB_DEST.
ENDLOOP
APPEND LINES OF TAB_SRC TO TAB_DEST.
Deleting a set of lines
Code:
LOOP AT TAB_DEST WHERE K=KVAL.
DELETE TAB_DEST.
ENDLOOP
DELETE TAB_DEST WHERE K=KVAL.
Tools available in SAP to pin-point a performance problem
Code:
The runtime analysis (SE30)
Code:
SQL Trace (ST05)
Code:
Tips and Tricks tool
Code:
The performance database
Optimizing the load of the database
Using table buffering
Using buffered tablesimproves the performance considerably. Note that in some cases a stament can notbe used with a buffered table, so when using these staments the buffer will bebypassed. These staments are:
Select DISTINCT
ORDER BY / GROUP BY/ HAVING clause
Any WHERE clasuse that contains a subquery or IS NULL expression
JOIN s
A SELECT... FORUPDATE
If you wnat toexplicitly bypass the bufer, use the BYPASS BUFFER addition to the SELECRclause.
Use the ABAP SORTClause Instead of ORDER BY
The ORDER BY clause isexecuted on the database server while the ABAP SORT statement is executed on theapplication server. The datbase server will usually be the bottleneck, sosometimes it is better to move thje sort from the datsbase server to theapplication server.
If you are not sortingby the primary key ( E.g. using the ORDER BY PRIMARY key statement) but aresorting by another key, it could be better to use the ABAP SORT stament to sortthe data in an internal table. Note however that for very large result sets itmight not be a feasible solution and you would want to let the datbase serversort it.
Avoid ther SELECTDISTINCT Statement
As with the ORDER BYclause it could be better to avoid using SELECT DISTINCT, if some of the fieldsare not part of an index. Instead use ABAP SORT + DELETE ADJACENT DUPLICATES onan internal table, to delete duplciate rows.
TIPS & TRICKS FOR OPTIMIZATION
Use the GET RUN TIME command to help evaluate performance. It'shard to know whether that optimization technique REALLY helps unless you testit out. Using this tool can help you know what is effective, under what kindsof conditions. The GET RUN TIME has problems under multiple CPUs, so youshould use it to test small pieces of your program, rather than the wholeprogram.
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 expensiveoperations. Memory, if not controlled, may have to be written to swap space onthe hard disk, which therefore increases your I/O read/writes to disk. CPUactivity can be reduced by careful program design, and by using commands suchas 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. Thiscan 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 tomemory (internal tables use memory). For this reason, field-groups are onlyappropriate for processing large lists (e.g. over 50,000 records). If you havelarge lists, you should work with the systems administrator to decide themaximum amount of RAM your program should use, and from that, calculate howmuch space your lists will use. Then you can decide whether to write the datato memory or swap space.
Use as many table keys as possible in the WHERE part of your selectstatements.
Whenever possible, design the program to access a relatively constantnumber of records (for instance, if you only access the transactions for onemonth, then there probably will be a reasonable range, like 1200-1800, for thenumber of transactions inputted within that month). Then use a SELECT A B CINTO TABLE ITAB statement.
Get a good idea of how many records you will be accessing. Log into yourproductive system, and use SE80 -> Dictionary Objects (press Edit), enter thetable name you want to see, and press Display. Go To Utilities -> TableContents to query the table contents and see the number of records. This isextremely useful in optimizing a program's memory allocation.
Try to make the user interface such that the program gradually unfoldsmore information to the user, rather than giving a huge list of informationall at once to the user.
Declare your internal tables using OCCURS NUM_RECS, where NUM_RECS is thenumber of records you expect to be accessing. If the number of records exceedsNUM_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 ofthe records into the itab in one operation, rather than repeated operationsthat result from a SELECT A B C INTO ITAB... ENDSELECT statement. Make surethat ITAB is declared with OCCURS NUM_RECS, where NUM_RECS is the number ofrecords you expect to access.
If the number of records you are reading is constantly growing, you may beable to break it into chunks of relatively constant size. For instance, if youhave 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). Usethese avoid wasting resources by calculating a total that has already beencalculated and stored.
ABAP/4 Development Code EfficiencyGuidelines
ABAP/4 (Advanced Business Application Programming 4GL) language is an "event-driven", "top-down", well-structured and powerful programming language.
The ABAP/4 processor controls the execution of an event. Because the ABAP/4 language incorporates many "event" keywords and these keywords need not be in any specific order in the code, it is wise to implement in-house ABAP/4 coding standards.
SAP-recommended customer-specific ABAP/4 development guidelines can be found in the SAP-documentation.
This page contains some general guidelines for efficient ABAP/4 Program Development that should be considered to improve the systems performance on the following areas:-
Physical I/O - data must be read from and written into I/O devices. This can be a potential bottle neck. A well configured system always runs 'I/O-bound' - the performance of the I/O dictates the overall performance.
Memory consumption of the database resources eg. buffers, etc. CPU consumption on the database and application servers
Network communication - not critical for little data volumes, becomes a bottle neck when large volumes are transferred.
Policies and procedures can also be put into place so that every SAP-customer development object is thoroughly reviewed (quality - program correctness as well as code-efficiency) prior to promoting the object to the SAP-production system. Information on the SAP R/3 ABAP/4 Development Workbench programming tools and its features can be found on the SAP Public Web-Server.
--------------------------------------------------------------------------------
CLASSIC GOOD 4GL PROGRAMMING CODE-PRACTICES GUIDELINES
Avoid dead-code Remove unnecessary code and redundant processing Spend time documenting and adopt good change control practices Spend adequate time anayzing business requirements, process flows, data-structures and data-model Quality assurance is key: plan and execute a good test plan and testing methodology
Experience counts
--------------------------------------------------------------------------------
SELECT * FROM <TABLE>
CHECK: <CONDITION>
ENDSELECT
vs.
SELECT * FROM <TABLE>
WHERE <CONDITION>
ENDSELECT
In order to keep the amount of data which is relevant to the query the hit set small, avoid using SELECT+CHECK statements wherever possible. As a general rule of thumb, always specify all known conditions in the WHERE clause (if possible). If there is no WHERE clause the DBMS has no chance to make optimizations. Always specify your conditions in the Where-clause instead of checking them yourself with check-statements. The database system can also potentially make use a database index (if possible) for greater efficiency resulting in less load on the database server and considerably less load on the network traffic as well.
Also, it is important to use EQ (=) in the WHERE clause wherever possible, and analyze the SQL-statement for the optimum path the database optimizer will utilize via SQL-trace when necessary. Also, ensure careful usage of "OR", "NOT" and value range tables (INTTAB) that are used inappropriately in Open SQL statements.
--------------------------------------------------------------------------------
SELECT *
vs.
SELECT SINGLE *
If you are interested in exactly one row of a database table or view, use the SELECT SINGLE statement instead of a SELECT * statement. SELECT SINGLE requires one communication with the database system whereas SELECT * requires two.
--------------------------------------------------------------------------------
SELECT * FROM <TABLE> INTO <INT-TAB>
APPEND <INT-TAB>
ENDSELECT
vs.
SELECT * FROM <TABLE> INTO TABLE <INT-TAB>
It is usually faster to use the INTO TABLE version of a SELECT statement than to use APPEND statements
--------------------------------------------------------------------------------
SELECT ... WHERE + CHECK
vs.
SELECT using aggregate function
If you want to find the maximum, minimum, sum and average value or the count of a database column, use a select list with aggregate functions instead of computing the aggregates within the program. The RDBMS is responsible for aggregated computations instead of transferring large amount of data to the application. Overall Network, Application-server and Database load is also considerably less.
--------------------------------------------------------------------------------
SELECT INTO TABLE <INT-TAB> + LOOP AT T
::::
SELECT * FROM <TABLE> INTO TABLE <INT-TAB>.
LOOP AT <INT-TAB>.
ENDLOOP.
vs.
SELECT * FROM <TABLE>
:::.
ENDSELECT
If you process your data only once, use a SELECT-ENDSELECT loop instead of
collecting data in an internal table with SELECT ... INTO TABLE. Internal table
handling takes up much more space
--------------------------------------------------------------------------------
Nested SELECT statements:
SELECT * FROM <TABLE-A>
SELECT * FROM <TABLE-B>
::..
ENDSELECT.
ENDSELECT
vs.
Select with view
SELECT * FROM <VIEW>
ENDSELECT
To process a join, use a view wherever possible instead of nested SELECT statements.
Using nested selects is a technique with low performance. The inner select statement is executed several times which might be an overhead. In addition, fewer data must be transferred if another technique would be used eg. join implemented as a view in ABAP/4 Repository.
· SELECT ... FORM ALL ENTRIES
· Explicit cursor handling (for more information, goto Transaction SE30 - Tips &
Tricks)
--------------------------------------------------------------------------------
Nested select:
SELECT * FROM pers WHERE condition.
SELECT * FROM persproj WHERE person=pers-persnr.
... process ...
ENDSELECT.
ENDSELECT.
vs.
SELECT persnr FROM pers INTO TABLE ipers WHERE cond. :::.
SELECT * FROM persproj FOR ALL ENTRIES IN ipers
WHERE person=ipers-persnr
:::... process .:::::
ENDSELECT.
In the lower version the new Open SQL statement FOR ALL ENTRIES is used.
Prior to the call, all interesting records from 'pers' are read into an internal
table. The second SELECT statement results in a call looking like this (ipers
containing: P01, P02, P03):
(SELECT * FROM persproj WHERE person=P01')
UNION
(SELECT * FROM persproj WHERE person=P02')
UNION
(SELECT * FROM persproj WHERE person=P03')
In case of large statements, the R/3's database interface divides the statement into several parts and recombines the resulting set to one. The advantage here is that the number of transfers is minimized and there is minimal restrictions due to the statement size (compare with range tables).
--------------------------------------------------------------------------------
SELECT * FROM <TABLE>
vs.
SELECT <column(s)> FROM <TABLE>
Use a select list or a view instead of SELECT *, if you are only interested in specific columns of the table. If only certain fields are needed then only those fields should be read from the database. Similarly, the number of columns can also be restricted by using a view defined in ABAP/4 Dictionary. Overall database and network load is considerably less.
--------------------------------------------------------------------------------
SELECT without table buffering support
vs.
SELECT with table buffering support
For all frequently used, read-only(few updates) tables, do attempt to use SAP-buffering for eimproved performance response times. This would reduce the overall Database activity and Network traffic.
--------------------------------------------------------------------------------
Single-line inserts
LOOP AT <INT-TAB>
INSERT INTO <TABLE> VALUES <INT-TAB>
ENDLOOP
vs.
Array inserts
Whenever possible, use array operations instead of single-row operations to modify the database tables. Frequent communication between the application program and database system produces considerable overhead.
--------------------------------------------------------------------------------
Single-line updates
SELECT * FROM <TABLE>
<COLUMN-UPDATE STATEMENT>
UPDATE <TABLE>
ENDSELECT
vs.
Column updates
UPDATE <TABLE> SET <COLUMN-UPDATE STATEMENT>
Wherever possible, use column updates instead of single row updates to update your database tables
--------------------------------------------------------------------------------
DO....ENDDO loop with Field-Symbol
vs.
Using CA operator
Use the special operators CO, CA, CS instead of programming the operations yourself If ABAP/4 statements are executed per character on long strings, CPU consumprion can rise substantially
--------------------------------------------------------------------------------
Use of a CONCATENATE function module
vs.
Use of a CONCATENATE statement
Some function modules for string manipulation have become obsolete, and
should be replaced by ABAP statements or functions
STRING_CONCATENATE... ---> CONCATENATE
STRING_SPLIT... ---> SPLIT
STRING_LENGTH... ---> strlen()
STRING_CENTER... ---> WRITE..TO. ..CENTERED
STRING_MOVE_RIGHT ---> WRITE...TO...RIGHT-JUSTIFIED
--------------------------------------------------------------------------------
Moving with offset
vs.
Use of the CONCATENATE statement
Use the CONCATENATE statement instead of programming a string concatenation
of your own
--------------------------------------------------------------------------------
Use of SEARCH and MOVE with offset
vs.
Use of SPLIT statement
Use the SPLIT statement instead of programming a string split yourself
--------------------------------------------------------------------------------
Shifting by SY-FDPOS places
vs
Using SHIFT...LEFT DELETING LEADING...
If you want ot delete the leading spaces in a string use the ABAP/4 statements SHIFT...LEFT DELETING LEADING... Other constructions (with CN and SHIFT... BY SY-FDPOS PLACES, with CONDENSE if possible, with CN and ASSIGNCLA+SY-FDPOS(LEN) ...) are not as fast
--------------------------------------------------------------------------------
Get a check-sum with field length
vs
Get a check-sum with strlen ()
Use the strlen () function to restrict the DO loop to the relevant part of the field, eg. when determinating a check-sum
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