Cache Performance Tuning

Cache tuning example

As an example of how to tune Confluence's caches, let's have a look at the following table:

The maximum size of the caches above is 1000 (meaning that it can contain up to 1000 objects). You can tell when a cache size needs to be increased because the cache has both:

• a high usage percentage (above 75%)
• a low effectiveness percentage.

Check the 'effectiveness' versus the 'percent used'. A cache with a low percent used need not have its size lowered; it does not use more memory until the cache is filled.

Based on this, the sizes of the "Attachments", "Database Queries", and "Users" caches should be increased to improve their effectiveness.

As the stored information gets older or unused it will expire and be eliminated from the cache. Cache expiry may be based on time or on frequency of use.

There is not much that you can do with a cache that has both a low percentage of usage and effectiveness. Over time, as the cache is populated with more objects and repeat requests for them are made, the cache's effectiveness will increase.

Finding the configuration file

Cache configurations are stored in <confluence-home>/shared-home/config/cache-settings-overrides.properties 

For Confluence Data Center (clustered) it can be found in  <confluence-shared-home>/config/cache-settings-overrides.properties (in the shared home directory for the cluster).

Cache key mappings

The cache configuration file configures caches by their keys. To find out a cache key hover your mouse over the cache name in the Cache Management screen.

cacheKey.png [Added example of mousing-over a cache name to display its cache key.]

Caching in Confluence Data Center 

In Confluence Data Center (clustered) you have a distributed cache and a cluster node-local cache.  The Cluster Management page will indicate cluster distributed cache and cluster node-local cache. 

The cache configuration file is stored in the shared home directory for the cluster. 

Important caches

• Content Objects cache (com.atlassian.confluence.core.ContentEntityObject)
  should be set to at least 20-30% of the number of content entity objects (pages, comments, emails, news items) in your system. To find the number of content entity objects, use the query select count(*) from CONTENT where prevver is null.
• Content Body Mappings cache (com.atlassian.confluence.core.ContentEntityObject.bodyContents)
should be set to at least 20% of the number of content entity objects (pages, comments, emails, news items) in your system. To find the number of content entity objects, use the query select count(*) from CONTENT where prevver is null.

• Embedded Crowd Internal User cache (com.atlassian.crowd.model.user.InternalUser)
  should be set to the number of users you have in the internal directory.  You can discover this number by using the following SQL: 

  SELECT
      COUNT(*)
  FROM
      cwd_user u
  JOIN
      cwd_directory d
  ON
      u.directory_id = d.id
  AND d.directory_name = 'Confluence Internal Directory';

• Embedded Crowd Users cachecom.atlassian.confluence.user.crowd.CachedCrowdUserDao.USER_CACHE 
  should be set to the number of rows in the cwd_user table. 

  SELECT
   COUNT(*)
  FROM
   cwd_user u;

• Space permissions by ID cache (com.atlassian.confluence.security.SpacePermission) 
should be set to the number of space permissions in your deployment (a good rule of thumb is 20 times the number of spaces). You can find the number of space permissions using the query select count(*) from SPACEPERMISSIONS.

Monitoring the contents of a cache

To monitor what is in a cache:

1. In your browser go to <confluence-URL>/admin/cachecontents.jsp
   All caches that contain items will appear. 
2. Select a cache from the list. 

Notes

• To improve performance of a large Confluence site, we recommend that you move the caching of static content from the JVM into Apache. This will prevent the JVM from having a number of long running threads serving up static content. See Configuring Apache to Cache Static Content via mod_disk_cache.