PI72900: FF OF PI70095: IFI 306 READS TAKING LONGER, USING MORE CPU, REQUESTING MORE CLAIMS WHEN LOG RECORDS NEED TO DECOMPRESS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Performance degradation during IFI306 READS calls. Retrieving
  
  log records using IFI 306 READS can take longer and can use more
  
  CPU when the log records are compressed. To be able to
  
  decompress the log records the compression dictionary is
  
  required. To make the dictionary available and to guarantee
  
  that the correct dictionary is used, requires additional
  
  processing (which can result in a significant increase in CPU
  
  usage).
  
  Another symptom of this problem is a very large increase in the
  
  number of claim requests for threads issuing the IFI306
  
  requests (such as log read tasks of data replication products).
  
  Additional keywords: DB2STGLK/K
  

Local fix

• (1) If REORG is done by non-DB2 third party vendors, then
  
      specify KEEPDICTIONARY for CDC-enabled table spaces.
  
  (2) If REORG is done by V11 DB2 without KEEPDICTIONARY, then
  
      avoid deletion of SYSIBM.SYSCOPY rows with ICTYPE = J
  
      before replication.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Data Capture applications using IFI 306 to read compressed   *
  * log records from DB2 table spaces in DB2 V12.                *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Two problems when IFI 306 runs                               *
  * in DB2 for z/OS V12:                                         *
  * 1. Increased number of claims/declaims on pagesets under     *
  * certain circumstance during IFI 306.                         *
  * 2. Storage leak during IFI 306 if DB2 is unable to find the  *
  * archived dictionaries for older log records that need        *
  * decompression.                                               *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Increased number of claims/declaims on the pageset:          *
  * The code that finds the correct dictionary for decompression *
  * is called numerous times during IFI 306 READs, it results in *
  * increased number of Claims/Declaims since the code uses      *
  * Claim for serialization. This can happen under the following *
  * circumstances :                                              *
  * (A) Older dictionaries for the table spaces processed by IFI *
  * 306 cannot be found for some reason, in which   case the     *
  * code can be called for every single log record that needs    *
  * the older dictionary.                                        *
  * (B) IFI 306 is reading capture log records written for       *
  * concurrently running DML activities, in which case the code  *
  * can be called more often than normal.                        *
  * Storage leak :                                               *
  *                                                              *
  * During certain error conditions the storage allocated for    *
  * dictionaries did not get released on the assumption that it  *
  * would be released during commit or deallocate. But it did    *
  * not happen due to some missing control information.          *
  ****************************************************************
  

Problem conclusion

• Code has been updated to use CLAIM only when absolutely needed
  and to ensure that storage is released in the error path where
  it was not released before.
  

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:

  UI44236

Modules/Macros

• DSNIDCML DSNIFDIC
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RC10 PSY UI44236

     UP17/02/10 P F702

Fix is available

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