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+[[index-modules-cache]]
+== Cache
+
+There are different caching inner modules associated with an index. They
+include `filter` and others.
+
+[float]
+[[filter]]
+=== Filter Cache
+
+The filter cache is responsible for caching the results of filters (used
+in the query). The default implementation of a filter cache (and the one
+recommended to use in almost all cases) is the `node` filter cache type.
+
+[float]
+[[node-filter]]
+==== Node Filter Cache
+
+The `node` filter cache may be configured to use either a percentage of
+the total memory allocated to the process or an specific amount of
+memory. All shards present on a node share a single node cache (thats
+why its called `node``). The cache implements an LRU eviction policy:
+when a cache becomes full, the least recently used data is evicted to
+make way for new data.
+
+The setting that allows one to control the memory size for the filter
+cache is `indices.cache.filter.size`, which defaults to `20%`. *Note*,
+this is *not* an index level setting but a node level setting (can be
+configured in the node configuration).
+
+`indices.cache.filter.size` can accept either a percentage value, like
+`30%`, or an exact value, like `512mb`.
+
+[float]
+[[index-filter]]
+==== Index Filter Cache
+
+A filter cache that exists on the index level (on each node). Generally,
+not recommended for use since its memory usage depends on which shards
+are allocated on each node and its hard to predict it. The types are:
+`resident`, `soft` and `weak`.
+
+All types support the following settings:
+
+[cols="<,<",options="header",]
+|=======================================================================
+|Setting |Description
+|`index.cache.filter.max_size` |The max size (count, not byte size) of
+the cache (per search segment in a shard). Defaults to not set (`-1`),
+which is usually fine with `soft` cache and proper cacheable filters.
+
+|`index.cache.filter.expire` |A time based setting that expires filters
+after a certain time of inactivity. Defaults to `-1`. For example, can
+be set to `5m` for a 5 minute expiry.
+|=======================================================================
+