PM78087: IBM HTTP SERVER HIGH MEMORY USE WHEN MANY HUNDREDS OF REWRITECOND %{REQUEST_URI}

8.5.0.2: WebSphere Application Server V8.5 Fix Pack 2
8.0.0.6: WebSphere Application Server V8.0 Fix Pack 6

APAR status

• Closed as program error.

Error description

• IBM HTTP Server high memory use when many hundreds of
  RewrtieCond %{REQUEST_URI} are evaluated and the URL is very
  long.
  
  Typically, only a few conditions will be evaluated per
  request, because RewriteRule is supposed to screen out
  matching URL's. But if many conditions (hundreds) are attached
  to many rules which just pass everything through, a large
  amount of memory will be allocated.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:  Users of IBM HTTP Server with many hundreds *
  *                  of RewriteRules that always match and are   *
  *                  accompanied by RewriteCond's containing %   *
  *                  {REQUEST_URI} who are running out of        *
  *                  memory.                                     *
  ****************************************************************
  * PROBLEM DESCRIPTION: Configs with many mod_rewrite           *
  *                      directives can show high mem usage,     *
  *                      requiring MaxMemFree to be set to       *
  *                      avoid OutOfMemory conditions.           *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  mod_rewrite is optimized to short-circuit evaluation of
  RewriteCond when RewriteRules don't match, but some users
  configure catch-all RewriteRules and then rely on RewriteCond
  to do all of the checks.  This is exacerbated by not using the
  [L] flag to stop rewrite processing after a match.
  When hundreds of RewriteConds are evaluated, and they access a
  long URL via %{REQUEST_URI}, those copies of the URL cause the
  thread handling the request to allocate and set aside a lot of
  memory.
  Changing rules and conditions after the fact can be fragile.
  

Problem conclusion

• A "RewriteOption" sub-option, "NoCopy" was added to allow the
  specific lookup of %{REQUEST_URI} to not cause memory to be
  allocated.  This option is provided as a stop-gap measure when
  MaxMemFree cannot be used or is innefective, until the ruleset
  can be corrected to not cause the evaluation of many hundreds
  of conditions.
  
  This fix is targeted for IHS fixpacks:
   - 7.0.0.29
   - 8.0.0.6
   - 8.5.0.2
  

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

  IBM HTTP SERVER

• Fixed component ID

  5724J0801

Applicable component levels

• R700 PSY

     UP

• R800 PSY

     UP

• R850 PSY

     UP