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For all entries
Nested selects
Select using JOINS
Use the selection criteria
Use the aggregated functions
Select with view
Select with index support
Select … Into table
Select with selection list
Key access to multiple lines
Copying internal tables
Modifying a set of lines
Deleting a sequence of lines
Linear search vs. binary
Comparison of internal tables
Modify selected components
Appending two internal tables
Deleting a set of lines
Tools available in SAP to pin-point a performance problem
Optimizing the load of the database
Other General Tips & Tricks for Optimization
For all entries
The for all entries
creates a where clause, where all the entries in the driver table are combined with 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 of data
-
Mixing processing and
reading of data -
Fast internal reprocessing of data
-
Fast
The Minus
-
Difficult to program/understand
-
Memory could be critical (use FREE or PACKAGE size)
Some steps that might make FOR ALL ENTRIES more
efficient:
-
Removing
duplicates from the the driver table -
Sorting the driver table
-
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 of data
-
Mixing processing and reading of data
-
Easy to code - and understand
The minus:
-
Large amount of data
-
when mixed
processing isn’t needed -
Performance killer no. 1
Select using JOINS
The plus
-
Very large amount of data
-
Similar to Nested selects - when the accesses are planned by the programmer
-
In some cases the
fastest -
Not so
memory critical
The minus
-
Very
difficult to program/understand -
Mixing processing and reading of data not possible
Use the selection criteria
SELECT * FROM SBOOK.
CHECK: SBOOK-CARRID = 'LH' AND
SBOOK-CONNID = '0400'.
ENDSELECT. SELECT * FROM SBOOK
WHERE CARRID = 'LH' AND
CONNID = '0400'.
ENDSELECT.
Use the aggregated functions
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
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
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
REFRESH X006.
SELECT * FROM T006 INTO X006.
APPEND X006.
ENDSELECT
SELECT * FROM T006 INTO TABLE X006.
Select with selection list
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
LOOP AT TAB.
CHECK TAB-K = KVAL.
" ...
ENDLOOP.
LOOP AT TAB WHERE K = KVAL.
" ...
ENDLOOP.
Copying internal tables
REFRESH TAB_DEST.
LOOP AT TAB_SRC INTO TAB_DEST.
APPEND TAB_DEST.
ENDLOOP.
TAB_DEST[] = TAB_SRC[]. Modifying a set of lines
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
DO 101 TIMES.
DELETE TAB_DEST INDEX 450.
ENDDO.
DELETE TAB_DEST FROM 450 TO 550.
Linear search vs. binary
READ TABLE TAB WITH KEY K = 'X'.
READ TABLE TAB WITH KEY K = 'X' BINARY SEARCH. Comparison of internal tables
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
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
LOOP AT TAB_SRC.
APPEND TAB_SRC TO TAB_DEST.
ENDLOOP
APPEND LINES OF TAB_SRC TO TAB_DEST. Deleting a set of lines
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
-
The runtime analysis (SE30) -
SQL Trace (ST05) -
Tips and Tricks
tool -
The performance database
Optimizing the load of the
database
Using table
buffering
Using buffered tables
improves the performance considerably. Note that in some cases a stament can not be used with a buffered table, so when using these staments the
buffer will be bypassed. 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... FOR UPDATE
If you wnat to explicitly bypass the bufer,
use the BYPASS BUFFER addition to the SELECR clause.
Use the ABAP SORT Clause Instead of ORDER BY
The ORDER BY clause is executed on the database server while the ABAP SORT statement is executed
on the application server. The datbase server will usually be the bottleneck, so sometimes it is better to move thje sort from the datsbase
server to the application server.
If you are not sorting by the primary key ( E.g. using the ORDER BY PRIMARY key statement) but are sorting by another key, it could be better to
use the ABAP SORT stament to sort the data in an internal table. Note however that for very large result sets it might not be a feasible solution
and you would want to let the datbase server sort it.
Avoid ther SELECT DISTINCT Statement
As with the ORDER BY clause it could be better to avoid using SELECT DISTINCT, if some of the fields are not part of
an index. Instead use ABAP SORT + DELETE ADJACENT DUPLICATES on an internal table, to delete duplciate rows.
TIPS & TRICKS FOR OPTIMIZATION
- Use the GET RUN TIME command to help evaluate performance.
It's hard to know whether that optimization technique REALLY helps unless you test it out. Using this tool can help you know what is
effective, under what kinds of conditions. The GET RUN TIME has problems under multiple CPUs, so you should use it to test small pieces of
your program, rather than the whole program. - 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 expensive
operations. Memory, if not controlled, may have to be written to swap space on the hard disk, which therefore increases your I/O read/writes to
disk. CPU activity can be reduced by careful program design, and by using commands such as 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. This can 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 to memory (internal tables use memory). For this reason, field-groups are only
appropriate for processing large lists (e.g. over 50,000 records). If you have large lists, you should work with the systems administrator to
decide the maximum amount of RAM your program should use, and from that, calculate how much space your lists will use. Then you can decide
whether to write the data to memory or swap space. - Use as
many table keys as possible in the WHERE part of your select statements. - Whenever possible, design the program to access a relatively constant number of records (for instance, if you only access the
transactions for one month, then there probably will be a reasonable range, like 1200-1800, for the number of transactions inputted within
that month). Then use a SELECT A B C INTO TABLE ITAB statement. - Get a good idea of how many records you will be accessing. Log into your productive system, and use SE80 -> Dictionary Objects (press
Edit), enter the table name you want to see, and press Display. Go To Utilities -> Table Contents to query the table contents and see the
number of records. This is extremely useful in optimizing a program's memory allocation. - Try to make the user interface such that the program gradually unfolds more information to the user, rather than
giving a huge list of information all at once to the user. - Declare your internal tables using OCCURS NUM_RECS, where NUM_RECS is the number of records you expect to be accessing. If the number of
records exceeds NUM_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 of the records into the itab in one operation, rather
than repeated operations that result from a SELECT A B C INTO ITAB... ENDSELECT statement. Make sure that ITAB is declared with OCCURS
NUM_RECS, where NUM_RECS is the number of records you expect to access. - If the number of records you are reading is constantly growing, you may be able to break it into chunks of relatively constant
size. For instance, if you have 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). Use
these avoid wasting resources by calculating a total that has already been calculated and stored.
ABAP/4 Development Code Efficiency Guidelines
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 vs. SELECT * FROM In order to keep the amount of data which is relevant to the query the hit set small, avoid Also, it is important to use EQ (=) in the WHERE clause wherever possible, and analyze the SQL-statement for the Also, ensure -------------------------------------------------------------------------------- SELECT * vs. SELECT SINGLE * If you are interested in exactly one row of a database table or view, -------------------------------------------------------------------------------- SELECT vs. SELECT * FROM It is usually faster to use the INTO TABLE version of a SELECT statement than to use APPEND -------------------------------------------------------------------------------- SELECT ... WHERE + CHECK vs. SELECT using aggregate function If you want to -------------------------------------------------------------------------------- SELECT INTO TABLE vs. SELECT * FROM If you process your data only once, use a SELECT-ENDSELECT loop instead of collecting data in -------------------------------------------------------------------------------- Nested vs. Select with view To process a join, use a view wherever possible instead of nested SELECT · SELECT ... FORM ALL ENTRIES -------------------------------------------------------------------------------- Nested vs. SELECT persnr FROM pers In the lower version the new Open SQL statement FOR ALL ENTRIES is used. Prior to In case of large statements, the R/3's database -------------------------------------------------------------------------------- SELECT * FROM vs. SELECT Use a select list or a view instead of SELECT *, if you are only interested in specific columns of the -------------------------------------------------------------------------------- SELECT without table buffering support vs. SELECT with table buffering support For all -------------------------------------------------------------------------------- Single-line inserts 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 -------------------------------------------------------------------------------- Single-line updates vs. Column updates Wherever possible, use column -------------------------------------------------------------------------------- DO....ENDDO loop with Field-Symbol vs. Using CA operator Use the special operators CO, CA, CS instead of programming the -------------------------------------------------------------------------------- Use of a CONCATENATE function module vs. Use of a CONCATENATE statement Some function modules for string manipulation have STRING_CONCATENATE... ---> CONCATENATE -------------------------------------------------------------------------------- Moving vs. Use of the CONCATENATE Use the CONCATENATE statement instead of programming a string concatenation of -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Get a vs Get a Use the strlen () function to restrict the DO loop to the relevant part of the field, eg.
CHECK:
ENDSELECT
WHERE
ENDSELECT
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.
optimum path the database optimizer will utilize via SQL-trace when necessary.
careful usage of "OR", "NOT" and value range tables (INTTAB) that are used inappropriately in Open SQL statements.
use the SELECT SINGLE statement instead of a SELECT * statement. SELECT SINGLE requires one communication with the database system whereas
SELECT * requires two.
* FROM INTO
APPEND
ENDSELECT INTO TABLE
statements
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 * FROM INTO TABLE
LOOP AT
ENDLOOP.
……….
ENDSELECT
an internal table with SELECT ... INTO TABLE. Internal table handling takes up much more space
SELECT statements:
SELECT * FROM
SELECT * FROM
……..
ENDSELECT.
ENDSELECT
SELECT * FROM
ENDSELECT
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.
· Explicit cursor handling (for more information, goto Transaction SE30 – Tips & Tricks)
select:
SELECT * FROM pers WHERE condition.
SELECT * FROM persproj WHERE person = pers-persnr.
... process ...
ENDSELECT.
ENDSELECT.
INTO TABLE ipers WHERE cond. ……….
SELECT * FROM persproj FOR ALL ENTRIES IN ipers
WHERE person = ipers-persnr
………... process .……………
ENDSELECT.
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')
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).
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.
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.
LOOP AT
INSERT INTO VALUES
ENDLOOP
considerable overhead.
SELECT * FROM
UPDATE
ENDSELECT
UPDATE SET
updates instead of single row updates to update your database tables
operations yourself
If ABAP/4 statements are executed per character on long strings, CPU consumprion can rise substantially
become obsolete, and should be replaced by ABAP statements or functions
STRING_SPLIT... ---> SPLIT
STRING_LENGTH... ---> strlen()
STRING_CENTER... ---> WRITE..TO. ..CENTERED
STRING_MOVE_RIGHT ---> WRITE...TO...RIGHT-JUSTIFIED
with offset
statement
your own
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 ASSIGN CLA+SY-FDPOS(LEN) ...) are not as fast
check-sum with field length
check-sum with strlen ()
when determinating a check-sum
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