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:


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


The sampling rate for the request to be considered

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


An optional label for this LRU, to allow sharing an LRU across multiple remap rules. Note: In order for an LRU to be used by multiple remap rules, not only must the label match, both the --hits and --buckets options must be identical.


The minimum number of requests before promotion.


In addition to requests, also count bytes that are cache misses. If specified, default is 0, whichever triggers first of bytes and requests (hits) will cause promotion.


The size (number of entries) of the LRU.


Enables collecting statistics. The option requires an argument, the remap-identifier. The remap-identifier is a string that is concatenated to the stat name. The following stats are collected.

  • plugin.cache_promote.${remap-identifier}.cache_hits - Cache hit total, available for all policies.

  • plugin.cache_promote.${remap-identifier}.freelist_size - Size of the freelist when using the LRU policy.

  • plugin.cache_promote.${remap-identifier}.lru_size - Size of the LRU when using the LRU policy.

  • plugin.cache_promote.${remap-identifier}.lru_hit - LRU hit count when using the LRU policy.

  • plugin.cache_promote.${remap-identifier}.lru_miss - LRU miss count when using the LRU policy.

  • plugin.cache_promote.${remap-identifier}.lru_vacated - count of LRU entries removed to make room for a new request.

  • plugin.cache_promote.${remap-identifier}.promoted - count requests promoted, available in all policies.

  • plugin.cache_promote.${remap-identifier}.total_requests - count of all requests.


Allow cache promote to operate on internal (plugin-initiated) requests.

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


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

map \ @pparam=--policy=chance @pparam=--sample=10%

map \ @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.