PH57478: IFCID 199 DATA COLLECTION AND -DIS BP LSTATS INTERFERENCE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• There are different ways to obtain data set I/O statistics
  information in Db2. You ask for IFCID 199 to be written to SMF
  (or another trace destination) every STATIME (ZPARM) interval.
  You can also use IFI READS requests for IFCID 199. In that case
  the data is 'refreshed' every DSSTIME (ZPARM) interval. Lastly
  you can use -DIS BP .. LSTATS to obtain data set I/O statistics.
  
  With stats class 8 active you get IFCID 199 data every STATIME
  interval with dsn I/O stats info for that STATIME interval.
  With IFI READS for IFCID 199 you get dsn I/O stats for the last
  DSSTIME interval (data is updated every DSSTIME interval).
  With -DIS BP LSTATS you get dsn I/O stats since the last time
  the -DIS BP LSTATS command was executed.
  
  These interfaces uses a lot of common code under the covers.
  Unfortunately this can result is unexpected data if you use
  more than one of these techniques at the same time to obtain
  this info.
  For example, with STATIME=1 and statistics trace class 8 active,
  you expect data set I/O stats every minute (at the top of the
  minute) about the I/Os during the last minute. If you run
  -DIS BP LSTATS at 00:00:55 (5 sec before the top of the
  minute), the info in IFCID 199 at the top of the minute
  that follows at 00:01:00, will only contain I/Os that occurred
  in the last 5 seconds (since the -DIS BP LSTATS command ran)
  and not the I/OS of the last minute.
  Any of the 3 ways to collect data set I/O statistics will reset
  the data set I/O counters, so whatever process is used to
  collect this info, will only see the info about the I/Os since
  the last time any of these 3 ways to collect the info was
  invoked.
  

Local fix

• Only use one of the 3 ways to collect dsn I/O stats at a time
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All Db2 12 for z/OS and Db2 13 for z/OS      *
  *                 users with STATISTICS CLASS(8) trace         *
  *                 enabled and issues the Display Bufferpool    *
  *                 with LSTATS command                          *
  ****************************************************************
  * PROBLEM DESCRIPTION: Display Bufferpool LSTATS command       *
  *                      interferes with IFCID 199 collection    *
  *                      and reporting                           *
  ****************************************************************
  * RECOMMENDATION: Apply corrective PTF when available          *
  ****************************************************************
  Display Bufferpool LSTATS was interfering with IFCID 199
  statistics reporting of synchronous, asynchronous and
  zHyperlink I/O counts. Statistics were reset when Display
  Bufferpool LSTATS command was issued and when IFCID 199 were
  reported, causing the statistics to be incorrectly reported.
  

Problem conclusion

• Db2 has been corrected such that Display Bufferpool LSTATS and
  IFCID 199 reporting (when part of standard statistics as well
  as via READS requests) are separated.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UI99418 UI99419

Modules/Macros

• DSNB1DBP DSNB1TSD DSNB5CMX DSNB5COM DSNB5PCO DSNB5RAP DSNB5RDP
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RC10 PSY UI99418

     UP24/12/20 P F412

• RD10 PSY UI99419

     UP24/12/20 P F412

Fix is available

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