# Cache Promote Plugin¶

The cache_promote plugin provides a means to control when an object should be allowed to enter the cache. This is orthogonal from normal Cache-Control directives, providing a different set of policies to apply. The typical use case for this plugin is when you have a very large data set, where you want to avoid churning the ATS cache for the long tail content.

All configuration is done via remap.config, and the following options are available:

--policy

The promotion policy. The values lru and chance are supported.

--sample

The sampling rate for the request to be considered

If --policy is set to lru the following options are also available:

--hits

The minimum number of hits before promotion.

--buckets

The size (number of entries) of the LRU.

These two options combined with your usage patterns will control how likely a URL is to become promoted to enter the cache.

## Examples¶

These two examples shows how to use the chance and LRU policies, respectively:

map http://cdn.example.com/ http://some-server.example.com \
@plugin=cache_promote.so @pparam=--policy=chance @pparam=--sample=10%

map http://cdn.example.com/ http://some-server.example.com \
@plugin=cache_promote.so @pparam=--policy=lru \
@pparam=--hits=10 @pparam=--buckets=10000


Note --sample is available for all policies and can be used to reduce pressure under heavy load.