REG:REAL TIME QUE

Question

REAL TIME QUE
You are running a report. It is taking long time for
execution. What steps will you do to reduce the
execution time.
After running a BDC program in background, next
day morning when you see the results, few records
are not updated(error records). What will you do
then?
You are given functional specs for a BDC program
and you need to decide whether to write a method
call transaction or a session. How u will decide?
THANK YOU
ASHOK KUMAR

Answer 1

Hi,
For the first question, the solution can be as below with an example....
You can see a report performance in SE30(Runtime analysis)and
SQLtrace(ST05).
ST05 tells you the list of selected statements.
You should remember some points when you tuning the code
- 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.
Try to avoid joins more than 2 tables.
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 SELECT 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.
Reward points if useful...
Regards,
Sudha Mettu