Modelling your production system

Hello Blog readers,


Most of the times it is a real challenge to refresh data from production environment to test env with limited time and resources. But it is very important to know the future access path to be produced in production env while testing in development environment. This is basically needed to know the future performance problem associated due to access path chosen by the Optimizer.


Here is the extract of the DB2 administration guide which will guide you how to generate the exact access path in test system with respect to production system.

SELECT DISTINCT 'UPDATE SYSIBM.SYSTABLESPACE SET NACTIVEF='
CONCAT STRIP(CHAR(NACTIVEF))
CONCAT',NACTIVE='CONCAT STRIP(CHAR(NACTIVE))
CONCAT ' WHERE NAME=''' CONCAT TS.NAME
CONCAT ''' AND DBNAME ='''CONCAT TS.DBNAME CONCAT''';'
FROM SYSIBM.SYSTABLESPACE TS, SYSIBM.SYSTABLES TBL
WHERE TS.NAME = TSNAME
AND TBL.CREATOR IN (table creator_list)
AND TBL.NAME IN (table_list)
AND (NACTIVEF >=0 OR NACTIVE >=0);

==
SELECT 'UPDATE SYSIBM.SYSTABLES SET CARDF='
CONCAT STRIP(CHAR(CARDF))
CONCAT',NPAGES='CONCAT STRIP(CHAR(NPAGES))
CONCAT',PCTROWCOMP='CONCAT STRIP(CHAR(PCTROWCOMP))
CONCAT ' WHERE NAME='''CONCAT NAME
CONCAT ''' AND CREATOR ='''CONCAT CREATOR CONCAT''';'
FROM SYSIBM.SYSTABLES WHERE
CREATOR IN (creator_list)
AND NAME IN (table_list)
AND CARDF >= 0;
==
SELECT 'UPDATE SYSIBM.SYSINDEXES SET FIRSTKEYCARDF='
CONCAT STRIP(CHAR(FIRSTKEYCARDF))
CONCAT ',FULLKEYCARDF='CONCAT STRIP(CHAR(FULLKEYCARDF))
CONCAT',NLEAF='CONCAT STRIP(CHAR(NLEAF))
CONCAT',NLEVELS='CONCAT STRIP(CHAR(NLEVELS))
CONCAT',CLUSTERRATIO='CONCAT STRIP(CHAR(CLUSTERRATIO))
CONCAT',CLUSTERRATIOF='CONCAT STRIP(CHAR(CLUSTERRATIOF))
CONCAT' WHERE NAME='''CONCAT NAME
CONCAT ''' AND CREATOR ='''CONCAT CREATOR CONCAT''';'
FROM SYSIBM.SYSINDEXES
WHERE TBCREATOR IN (creator_list)
AND TBNAME IN (table_list)
AND FULLKEYCARDF >= 0;
==
SELECT 'UPDATE SYSIBM.SYSCOLUMNS SET COLCARDF='
CONCAT STRIP(CHAR(COLCARDF))
CONCAT',HIGH2KEY= X''' CONCAT HEX(HIGH2KEY)
CONCAT''',LOW2KEY= X''' CONCAT HEX(LOW2KEY)
CONCAT''' WHERE TBNAME=''' CONCAT TBNAME CONCAT ''' AND COLNO='
CONCAT STRIP(CHAR(COLNO))
CONCAT ' AND TBCREATOR =''' CONCAT TBCREATOR CONCAT''';'
FROM SYSIBM.SYSCOLUMNS
WHERE TBCREATOR IN (creator_list)
AND TBNAME IN (table_list)
AND COLCARDF >= 0;

SYSTABSTATS and SYSCOLDIST require deletes and inserts.
Delete statistics from SYSTABSTATS on the test subsystem for the specified tables
by using the following statement:
DELETE FROM (TEST_SUBSYSTEM).SYSTABSTATS
WHERE OWNER IN (creator_list)
AND NAME IN (table_list);

Use INSERT statements to repopulate SYSTABSTATS with production statistics that
are generated from the following statement:

SELECT 'INSERT INTO SYSIBM.SYSTABSTATS'
CONCAT '(CARD,NPAGES,PCTPAGES,NACTIVE,PCTROWCOMP'
CONCAT ',STATSTIME,IBMREQD,DBNAME,TSNAME,PARTITION'
CONCAT ',OWNER,NAME,CARDF) VALUES('
CONCAT STRIP(CHAR(CARD)) CONCAT ' ,'
CONCAT STRIP(CHAR(NPAGES)) CONCAT ' ,'
CONCAT STRIP(CHAR(PCTPAGES)) CONCAT ' ,'
CONCAT STRIP(CHAR(NACTIVE)) CONCAT ' ,'
CONCAT STRIP(CHAR(PCTROWCOMP)) CONCAT ' ,'
CONCAT '''' CONCAT CHAR(STATSTIME) CONCAT ''' ,'
CONCAT '''' CONCAT IBMREQD CONCAT ''' ,'
CONCAT '''' CONCAT STRIP(DBNAME) CONCAT ''' ,'
CONCAT '''' CONCAT STRIP(TSNAME) CONCAT ''' ,'
CONCAT STRIP(CHAR(PARTITION)) CONCAT ' ,'
CONCAT '''' CONCAT STRIP(OWNER) CONCAT ''' ,'
CONCAT '''' CONCAT STRIP(NAME) CONCAT ''' ,'
CONCAT STRIP(CHAR(CARDF)) CONCAT ');'
FROM SYSIBM.SYSTABSTATS
WHERE OWNER IN (creator_list)
AND NAME IN (table_list);

==
Delete statistics from SYSCOLDIST on the test subsystem for the specified tables
by using the following statement:
DELETE FROM (TEST_SUBSYSTEM).SYSCOLDIST
WHERE TBOWNER IN (creator_list)
AND TBNAME IN (table_list);

Use INSERT statements to repopulate SYSCOLDIST with production statistics that
are generated from the following statement:

SELECT 'INSERT INTO SYSIBM.SYSCOLDIST '
CONCAT '(FREQUENCY,STATSTIME,IBMREQD,TBOWNER'
CONCAT ',TBNAME,NAME,COLVALUE,TYPE,CARDF,COLGROUPCOLNO'
CONCAT ',NUMCOLUMNS,FREQUENCYF) VALUES( '
CONCAT STRIP(CHAR(FREQUENCY)) CONCAT ' ,'
CONCAT '''' CONCAT CHAR(STATSTIME) CONCAT ''' ,'
CONCAT '''' CONCAT IBMREQD CONCAT ''' ,'
CONCAT '''' CONCAT STRIP(TBOWNER) CONCAT ''' ,'
CONCAT '''' CONCAT STRIP(TBNAME) CONCAT ''','
CONCAT '''' CONCAT STRIP(NAME) CONCAT ''' ,'
CONCAT 'X''' CONCAT STRIP(HEX(COLVALUE)) CONCAT ''' ,'
CONCAT '''' CONCAT TYPE CONCAT ''' ,'
CONCAT STRIP(CHAR(CARDF)) CONCAT ' ,'
CONCAT 'X'''CONCAT STRIP(HEX(COLGROUPCOLNO)) CONCAT ''' ,'
CONCAT CHAR(NUMCOLUMNS) CONCAT ' ,'
CONCAT STRIP(CHAR(FREQUENCYF)) CONCAT ');'
FROM SYSIBM.SYSCOLDIST
WHERE TBOWNER IN (creator_list)
AND TBNAME IN (table_list);


Note about SPUFI:

• If you use SPUFI to execute the preceding SQL statements, you might need to increase the default maximum character column width to avoid truncation.
• Asterisks (*) appear in the examples to avoid having the semicolon interpreted as the end of the SQL statement. Edit the result to change the asterisk to a semicolon.

Access path differences from test to production: When you bind applications on the
test system with production statistics, access paths should be similar but still may
be different to what you see when the same query is bound on your production
system.

The access paths from test to production could be different for the following possible reasons:

• The processor models are different.
• The number of processors are different. (Differences in the number of processors can affect the degree of parallelism that is obtained.)
• The buffer pool sizes are different.
• The RID pool sizes are different.
• Data in SYSIBM.SYSCOLDIST is mismatched. (This mismatch occurs only if some of the previously mentioned steps mentioned are not followed exactly).
• The service levels are different.
• The values of optimization subsystem parameters, such as STARJOIN, NPGTHRSH, and PARAMDEG (MAX DEGREE on installation panel DSNTIP8) are different.
• v The use of techniques such as optimization hints and volatile tables are different.

Tools to help: If your production system is accessible from your test system, you
can use DB2 PM EXPLAIN on your test system to request EXPLAIN information
from your production system. This request can reduce the need to simulate a
production system by updating the catalog.

You can also use the DB2 Visual Explain feature to display the current
PLAN_TABLE output or the graphed access paths for statements within any
particular subsystem from your workstation environment. For example, if you have
your test system on one subsystem and your production system on another
subsystem, you can visually compare the PLAN_TABLE outputs or access paths
simultaneously with some window or view manipulation. You can then access the
catalog statistics for certain referenced objects of an access path from either of the
displayed PLAN_TABLEs or access path graphs.

Cheers...
Prakash C. Singh
IBM Certified DB2 DBA