Sun Java System Web Server 6.1 SP6 Performance Tuning, Sizing, and Scaling Guide

Tuning the ACL User Cache

The ACL user cache is on by default. Because of the default size of the cache (200 entries), the ACL user cache can be a bottleneck, or can simply not serve its purpose on a site with heavy traffic. On a busy site, more than 200 users can hit ACL-protected resources in less time than the lifetime of the cache entries. When this situation occurs, Sun Java System Web Server must query the LDAP server more often to validate users, which impacts performance.

This bottleneck can be avoided by increasing the size of the ACL cache with the ACLUserCacheSize directive in magnus.conf. Note that increasing the cache size will use more resources; the larger you make the cache, the more RAM you'll need to hold it.

There can also be a potential (but much harder to hit) bottleneck with the number of groups stored in a cache entry (4 by default). If a user belongs to 5 groups and hits 5 ACLs that check for these different groups within the ACL cache lifetime, an additional cache entry is created to hold the additional group entry. When there are 2 cache entries, the entry with the original group information is ignored.

While it would be extremely unusual to hit this possible performance problem, the number of groups cached in a single ACL cache entry can be tuned with the ACLGroupCacheSize directive.

This section includes the following topics:

ACL User Cache Directives

To adjust the ACL user cache values you must manually add the following directives to your magnus.conf file:


Set this directive to a number that determines the number of seconds before the cache entries expire. Each time an entry in the cache is referenced, its age is calculated and checked against ACLCacheLifetime. The entry is not used if its age is greater than or equal to the ACLCacheLifetime. The default value is 120 seconds. If this value is set to 0, the cache is turned off. If you use a large number for this value, you may need to restart Sun Java System Web Server when you make changes to the LDAP entries. For example, if this value is set to 120 seconds, Sun Java System Web Server might be out of sync with the LDAP server for as long as two minutes. If your LDAP is not likely to change often, use a large number.


Set this directive to a number that determines the size of the User Cache (default is 200).


Set this directive to a number that determines how many group IDs can be cached for a single UID/cache entry (default is 4).

Verifying ACL User Cache Settings

With LogVerbose you can verify that the ACL user cache settings are being used. When LogVerbose is running, you should expect to see these messages in your errors log when the server starts:

User authentication cache entries expire in ### seconds.
User authentication cache holds ### users.
Up to ### groups are cached for each cached user.


You can turn LogVerbose on by:

Note –

Do not turn on LogVerbose on a production server. Doing so degrades performance and greatly increases the size of your error logs.