A fix is available
APAR status
Closed as new function.
Error description
Initial zparms simplification enhancements
Local fix
N/A
Problem summary
**************************************************************** * USERS AFFECTED: * * All Db2 12 for z/OS customers. * **************************************************************** * PROBLEM DESCRIPTION: * * This APAR provides updated ranges and * * default settings for selected Db2 12 * * subsystem (DSNZPxxx) parameters. * **************************************************************** * RECOMMENDATION: * **************************************************************** A review of Db2 subsystem parameters reveals some that accept settings or have default settings that do not comply with Db2 best practices: CHKFREQ - specifies, when single checkpoint mode is in effect, either the number of log records written between checkpoints (if 1000 - 16000000) or the number of minutes between checkpoints (if 1 to 60). Current good practice for time-oriented checkpoint intervals is to take a checkpoint at least every 3 minutes. The current CHKFREQ default of 5 minutes does not agree with the best practice of taking a checkpoint every 3 minutes. CHKMINS - specifies, when dual checkpoint mode is in effect, the number of minutes between checkpoints (1 to 1439). Current good practice for time-oriented checkpoint intervals is to take a checkpoint at least every 5 minutes. PCLOSET - specifies the number of minutes that a partition or page set remains read-write after it is updated and before it is converted to read-only. The current default setting is 10 minutes but Db2 best practice is 45 minutes. MAXRBLK - specifies the amount of storage in kilobytes that is needed for the RID pool. The current default setting is 400000 KB but with todays greater data volume and increased storage availability, the Db2 best practice is 1000000 KB. NPGTHRSH - specifies whether Db2 favors matching index access, through the index with the most matching columns, for tables or partitions that have fewer data pages than the specified value. The current default of 0 means that Db2 always chooses the access path based on cost estimates, regardless of the number of data pages that statistics indicate for the table or partition. However, Db2 recommends use of NPGTHRSH=1 so that matching index access can be chosen when statistics for a table space or partition show that it is empty or when statistics show the default. INLISTP - the maximum number of elements in an IN-list for certain IN predicate optimizations to occur. The current default of 50 elements does not reflect the current best practice recommendation of 1000. The sample DSNTIJUZ job in prefix.SDSNSAMP(DSNTIJUZ) contains an extraneous continuation character 'X' in column 72 following the keyword parameter XML_RANDOMIZE_DOCID=NO. This issue does not affect DSNTIJUZ jobs that have been edited by the Db2 installation CLIST.
Problem conclusion
Temporary fix
Comments
************************************** In response, this APAR updates the default setting - or in some cases the range of acceptable settings - of each the following parameters: CHKFREQ - The default setting is changed from 5 minutes to 3. Also, values from 6 to 60 minutes are no longer documented as valid and are no longer accepted by the MINUTES/CHECKPOINT field on installation panel DSNTIPL1 when the CHECKPOINT TYPE field is set to MINUTES. When CHKTYPE=SINGLE, DSN6SYSP still accepts CHKFREQ values from 6 to 60 for compatibility reasons but converts them to 5, writes the following message during assembly, and sets the minimum return code to 4: 'CHKFREQ WAS DECREASED FROM n TO 5, THE MAXIMUM CHECKPOINT SETTING IN MINUTES' where 'n' is the specified CHKFREQ setting. CHKMINS - Values from 6 to 1439 minutes are no longer documented as valid and are no longer accepted by the MINUTES/CHECKPOINT field on installation panel DSNTIPL1 when the CHECKPOINT TYPE field is set to BOTH. When CHKTYPE=BOTH, DSN6SYSP still accepts values from 6 to 1439 for compatibility reasons but converts them to 5, writes the following message during assembly, and sets the minimum return code to 4: 'CHKMINS WAS DECREASED FROM n TO 5, THE MAXIMUM CHECKPOINT SETTING IN MINUTES' where 'n' is the specified CHKMINS setting. PCLOSET - The default setting is changed from 10 minutes to the Db2 best-practices value of 45. MAXRBLK - The default setting is changed from 400000 kilobytes to the Db2 best-practices value of 1000000 kilobytes. NPGTHRSH - The default setting is changed from 0 to the Db2 best-practices value of 1. INLISTP - The default setting is changed from 50 to the Db2 best-practices value of 1000. Review your current Db2 subsystem parameter settings with respect to the above changes to determine if you should update your current settings to comply with Db2 good practice recommendations. Applying the PTF for this APAR does not directly modify your Db2 configuration. However, it will be affected the next time you rebuild your subsystem parameter (DSNZPxxx) module if you specify one or more of the following parameters in the ranges indicated: CHKFREQ in the range of 6 to 60 (when CHKTYPE=SINGLE): These settings will be converted to 5 during subsystem parameter assembly with the warning message noted above. Following the next use of the -SET SYSPARM command or Db2 restart, Db2 will take more frequent checkpoints than previously. CHKMINS in the range of 6 to 1439 (when CHKTYPE=BOTH): These settings will be converted to 5 during subsystem parameter assembly with the warning message noted above. Following the next use of the -SET SYSPARM command or Db2 restart, Db2 will take more frequent checkpoints than previously. This APAR also modifies the sample DSNTIJUZ job in prefix.SDSNSAMP to remove the extraneous continuation character 'X' in column 72 after the keyword parameter XML_RANDOMIZE_DOCID=NO.
APAR Information
APAR number
PH21370
Reported component name
DB2 OS/390 & Z/
Reported component ID
5740XYR00
Reported release
C10
Status
CLOSED UR1
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2020-01-23
Closed date
2020-03-16
Last modified date
2020-04-02
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UI68424
Modules/Macros
DSN6SPRM DSNTIPL1 DSNTXAZP DSN6SYSP DSNTIDXA DSNTIJUZ DSNTINST DSNTIDXC DSNTIDXB DSN@XAZP
Fix information
Fixed component name
DB2 OS/390 & Z/
Fixed component ID
5740XYR00
Applicable component levels
RC10 PSY UI68424
UP20/03/25 P F003
Fix is available
Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.
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Document Information
Modified date:
25 March 2020