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Subject DO NOT REPLY [Bug 46749] New: Ldap cache cleaning is broken when LDAPSharedCacheSize is too small
Date Sat, 21 Feb 2009 11:12:20 GMT

           Summary: Ldap cache cleaning is broken when LDAPSharedCacheSize
                    is too small
           Product: Apache httpd-2
           Version: 2.3-HEAD
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: mod_ldap

util_ald_cache_purge() is only called when the max number of entries as defined
by LDAPCacheEntries/ LDAPOpCacheEntries is reached. If LDAPSharedCacheSize is
too small and the max number of entries is never reached, the ldap cache is
never purged and the cache hit rate drops rapidly.

The comment "/* should be safe to add an entry */" in util_ldap_cache_mgr.c is
simply wrong. At the very least, there should be a warning logged when memory
allocation fails. Also, a cache purge should be triggered in this case. When
the cache is filled less than the 3/4 watermark, it is not possible to do the
normal purge. In this case it may make sense to just purge the whole cache.
This will still yield a higher cache hit rate than leaving old entries in the
cache indefinitely.

Maybe the LDAPCacheEntries/ LDAPOpCacheEntries could also be adjusted
automatically, but this may be problematic as (AFAICS) all caches share the
same shared memory segment.

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