Re: bypassing buffer

Former Member — Thu, 02 Aug 2007 09:41:34 GMT

Performance Tunning is the process of tunning our queries etc to increase the performance of our object.

Some of the tips to increase ABAP performnace.

• 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.

• 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. See the Fieldgroups ABAP example.

• 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.

• 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 PERFORMANCE IMPROVEMENTS VIA DATA DICTIONARY

• INDEX CREATION SUGGESTIONS RELATED TO DATABASE PERFORMANCE

• The columns at the beginning of an index are the most “common”. The most “common” columns are those where reports are selecting columns with no ranges - the where clause for these columns is an “equal to” expression. Rearrange columns of an index to match the selection criteria. For example, if a select statement is written to include columns 1 and 2 with “equal to” expressions in the where clause and column 3 and 4 are selected with value ranges, then the index should be created with columns in the sequence of 1,2,3,4.

• Columns towards the end of the index are either infrequently used in selects or are part of reporting selects that involve ranges of values.

• TABLE TYPE SUGGESTIONS RELATED TO DATABASE PERFORMANCE

• Use VIEW tables to effectively join and “denormalize” related tables that are taking large amounts of time to select for reporting. For example, at times where highly accessed tables normalize description text into one table and the header data into another table, it may make sense to create a view table that joins the relevant fields of the two associated with a poor performing ABAP.

• For POOL tables that contain large amounts of data and are highly accessed, convert the pooled table into a transparent table and add an index. POOLED tables are supposed to be collections of smaller tables that are quickly accessed from the database or are completely buffered in memory. Pooled tables containing more than a few hundred rows and are accessed many times in a report or transaction are candidates for POOL to TRANSPARENT Conversion. For example, table A053 contains tax jurisdiction condition information and are accessed more than ten times in the sales order create transaction. If the entire United States tax codes are loaded into these condition tables, the time to save a sales order increases to unacceptable levels. Converting the tax condition table to transparent and creating an index based upon the key fields, decreases processing time from minutes to seconds.

• Do not allow the use of LIKE in an SAP SQL statement accessing a large table.

• Use internal tables in ABAPs to preselect values once and store values in memory for sorting and searching purposes (this is an assumption stated at the beginning of this discussion).

• Avoid logical databases when not processing all row s of a table. In fact, a logical database is merely a group of nested SAP SQL SELECT statements. In general, when processing a small number of rows in a larger table is required, the use of internal tables and NOT using a logical database or nested selects will be much better for performance.

Check the following Links

http://www.sapgenie.com/abap/performance.htm

http://www.thespot4sap.com/Articles/SAPABAPPerformanceTuning_PerformanceAnalysisTools.asp

check the below link

http://www.sap-img.com/abap/performance-tuning-for-data-selection-statement.htm

See the following link if it's any help:

http://www.thespot4sap.com/Articles/SAPABAPPerformanceTuning_PerformanceAnalysisTools.asp

Check also http://service.sap.com/performance

and

books like

http://www.sap-press.com/product.cfm?account=&product=H951

http://www.sap-press.com/product.cfm?account=&product=H973

http://www.sap-img.com/abap/more-than-100-abap-interview-faqs.htm

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

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 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.

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 statement can not be used with a buffered table, so when using these statements the buffer will be bypassed. These statements are:

Select DISTINCT

ORDER BY / GROUP BY / HAVING clause

Any WHERE clause that contains a sub query or IS NULL expression

JOIN s

A SELECT... FOR UPDATE

If you wan t to explicitly bypass the buffer, 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 database server will usually be the bottleneck, so sometimes it is better to move the sort from the database 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 statement 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 database server sort it.

Avoid the 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 duplicate rows.

Check this link...

http://www.sapdevelopment.co.uk/perform/performhome.htm

These are the internal pages of the above link

http://www.sapdevelopment.co.uk/perform/perform_pcursor.htm

http://www.sapdevelopment.co.uk/perform/perform_rtacode.htm

http://www.sapdevelopment.co.uk/perform/perform_sqltrace.htm

http://www.sapdevelopment.co.uk/perform/perform_groupby.htm

Go through the following Document

Check the following Links

http://www.sapgenie.com/abap/performance.htm

http://www.thespot4sap.com/Articles/SAPABAPPerformanceTuning_PerformanceAnalysisTools.asp

check the below link