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+---
+summary: Cache presence incoming presence
+...
+
+Introduction
+============
+
+This module stores presence from users contact even when they are
+offline, so that the client can see who is online faster when they sign
+in, and won't have to wait for remote servers to reply.
+
+Note that in its current form, the number of presence stanzas sent to a
+client is doubled, as the client would get both the cached stanzas and
+replies to presence probes. Also see [mod\_throttle\_presence].
+
+By default, only binary (online or offline) state is stored. It can
+optionally store the full presence but this requires much more memory.
+
+Configuration
+=============
+
+Just enable the module.
+
+    modules_enabled = {
+        -- more modules
+        "presence_cache";
+    }
+
+Advanced configuration
+======================
+
+To enable full stanza caching:
+
+    presence_cache_full = false
+
+TODO
+====
+
+-   Deduplication, i.e don's send stanzas that are identical to the last
+    seen.
+-   Cache invalidation or expiry, eg if a remote server goes down or is
+    gone a long time.
+-   Sending probes at some interval to keep the cache reasonably fresh.
+
+