PH35234: HIGH CPU ISSUE WHEN THE WEB URI PMI URL IS ENABLED

APAR status

• Closed as program error.

Error description

• PMI infrastructure does not scale well when the URL grows
  unbounded.
  When PMI StatisticSet is set to Custom, which
  enables the PMI webAppModule counters by default. In some cases
  the high CPU usage may be driven by the PMI webAppModule
  counters (RequestCount, ConcurrentRequests, and ServiceTime).
  

Local fix

• Disable equestCount, ConcurrentRequests, and ServiceTime URL
  related Web Application PMI counters, they will not have this
  problem. It is not usually common, as many customers do not
  enable these counters in PMI, as it is known to have a
  performance impact.
  
  For more information, please refer to the
  following Knowledge Center documentation, which lists the
  impact on enabling Web application counters:
  
  https://www.ibm.co
  m/support/knowledgecenter/en/SSAW57_8.5.5/com.ibm.websphere.nd.m
  ultiplatform.doc/ae/rprf_datacounter10.html
  
  Hence, if the
  customer wants to continue using PMI, and not experience high
  CPU usage, without disabling IM, we recommend them to disable
  the above webAppModules, by following the steps below:
  
  1) In
  the admin console, on the left hand side, select the
  following:
  
  Monitoring and Tuning -> Performance Monitoring
  Infrastructure (PMI)
  
  2) Choose the correct application
  server.
  
  3) Ensure Enable PMI is checked. (I assume it is since
  you're even
  
  seeing an issue with PMI)
  
  4) Click on Custom.
  (This is a link to a customization area)
  
  5) On the left hand
  side of the customization area, choose Web
  
  Applications.
  
  6)
  Select URIConcurrentRequests (ID=16), URIServiceTime (ID=17),
  URIRequestCount (ID=15) and AsyncContext Response Time
  (ID=19)
  
  Choose Disable.
  
  7) Save the changes , re-sync all
  nodes and restart the server.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:  All users of IBM WebSphere Application      *
  *                  Server                                      *
  ****************************************************************
  * PROBLEM DESCRIPTION: A high CPU issue may be seen when PMI   *
  *                      URL                                     *
  *                      statistic counters grow unbounded.      *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  When the PMI URL statistic counters are enabled for unbounded
  URLs, a high CPU issue may be encountered. It is not
  recommended for users to have individual URL statistics
  enabled for increasing and unbounded URLS (and users may not
  be able to pinpoint the source of their high CPU issue), so a
  warning message has been added telling users to disable
  specific PMI statistic counters after the
  counter has tracked over 5000 (as a default) different URLs.
  The value of the default can be changed by setting the system
  property com.ibm.ws.pmi.maxUniquePmiMetricCount.
  An example of the warning:
  CWPMI0109W: Over {0} stats are being tracked for {1}, PMI
  module {2} id {3}. By tracking a high number of PMI metrics,
  performance issues can occur. Disable {1}, PMI module {2} ID
  {3} in the administrative console.
  

Problem conclusion

• The fix for this APAR is targeted for inclusion in fix packs
  8.5.5.24 and 9.0.5.15. 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

  WEBS APP SERV N

• Fixed component ID

  5724H8800

Applicable component levels