DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

SORTOUT DD UNIT=SYSDA,SPACE=(CYL,(5,2)),VOL=SER=SCR03
//SYSERR DD UNIT=SYSDA,SPACE=(CYL,(5,2)),VOL=SER=SCR03
//SYSIN DD *
LISTDEF CHKIDXB_LIST INCLUDE INDEXSPACE DBOT55*.* ALL
CHECK INDEX LIST CHKIDXB_LIST SHRLEVEL CHANGE
WORKDDN SYSUT1
SORTDEVT SYSDA
SORTNUM 4
/*
You should estimate the size of the sort work file which you write in the SORTWKnn DD
statement of the JCL. If a sort is required, you must provide the DD statement that the sort
program requires for the temporary data sets.
Note: To find the size of the sort work, the following steps should be taken.
1. For each table, multiply the number of records in the table by the number of indexes on
the table that need to be checked.
2. Add the products that you obtain in step 1.
3. Add 8 to the length of the longest key. For non padded indexes, the length of the longest
key is the maximum possible length of the key with all varying-length columns in the key
padded to their maximum length, plus 2 bytes for each varying-length column.
4. Multiply the sum from step 2 by the sum from step 3.
Availability enhancement
To improve availability, the DRAIN_WAIT, RETRY, and RETRY_DELAY parameters were
added to CHECK INDEX. This is similar to online REORG. Rather than waiting the lock time
out time, the utility multiplier for threads to relinquish the write claim, the utility will wait the
DRAIN_WAIT value to get all writers drained and if the drain is not successful, wait the
specified delay, and then retry the specified number of times. This will lessen the impact on
applications when the utility is unable to drain all objects.
Recommendation in creating shadow data sets
When you execute the CHECK INDEX utility with the SHRLEVEL CHANGE option, the utility
uses shadow data sets. For user-managed data sets, you must preallocate the shadow data
sets before you execute CHECK INDEX SHRLEVEL CHANGE.
If a table space, partition, or index that resides in DB2-managed data sets and shadow data
sets does not already exist when you execute CHECK INDEX, DB2 creates the shadow data
sets. At the end of CHECK INDEX processing, the DB2-managed shadow data sets are
deleted. We recommend you create the shadow data set in advance for DB2-managed data
sets also, especially for the shadow data sets of the logical partitions of non-partitioned
secondary indexes.
See DB2 UDB for z/OS Version 8 Utility Guide and Reference, SC18-7427, for more
information about this topic.
6.1.1 Performance measurement
Several performance studies have been done about online CHECK INDEX. Here we describe
the measurement environment and results.
Test environment and scenarios
264 DB2 UDB for z/OS Version 8 Performance Topics