PH27734: ZWAS POOR FILESYSTEM PERFORMANCE DUE TO CKACCESS / FSACCESS CML LOCK CONTENTION

APAR status

• Closed as program error.

Error description

• Under heavy load it is possible to see poor filesystem
  performance in zWAS servants due to CML lock contention on
  ckaccess paths for RACF class FSACCESS.
  Dump systrace analysis
  shows 2 CML lock obtains for the ZFS address space for each
  ckaccess request.
  
  This APAR was taken to call
  RACROUT
  REQUEST=LIST,...CLASS=FSACCESS
  during zWAS servant
  initialisation.
  
  This will reduce the number of CML lock
  obtains from RACF code on this path.
  

Local fix

• Disable FSACCESS checking in RACF.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:  All users of IBM WebSphere Application      *
  *                  Server                                      *
  *                  V9.0                                        *
  ****************************************************************
  * PROBLEM DESCRIPTION: WebSphere Application Server for z/OS   *
  *                      poor performance with FSACCESS profile  *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The FSACCESS profile is used to control access to the file
  system.  The CML lock is used to make the access checks even if
  the profile is RACLIST'd.  This caused significant delays when
  under load.
  

Problem conclusion

• Code was modified in the Servant address space to issue a
  RACROUT REQUEST=LIST for class FSACCESS during the Servant
  initialization if a new environment variable is set to "1".
  
  The RACROUT REQUEST=LIST issued within the Servant address
  space creates a local copy of the profile information within
  private storage of the Servant.  Access checks made on the
  FSACCESS class from the Servant will use this private storage
  without the need to obtain the CML lock.
  
  The new environment variable is
  server_region_racroute_list_fsaccess.  The default value is
  "0".
  
  The fix for this APAR is targeted for inclusion in fix pack
  9.0.5.7. For more information, see 'Recommended Updates for
  WebSphere Application Server':
  https://www.ibm.com/support/pages/node/715553
  

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:

Fix information

• Fixed component name

  WEBSPHERE FOR Z

• Fixed component ID

  5655I3500

Applicable component levels