1 files changed, 57 insertions, 0 deletions
diff --git a/synapse/util/caches/__init__.py b/synapse/util/caches/__init__.py
index 1a14904194..d53569ca49 100644
--- a/synapse/util/caches/__init__.py
+++ b/synapse/util/caches/__init__.py
@@ -14,6 +14,10 @@
 # limitations under the License.
 
 import synapse.metrics
+from lrucache import LruCache
+import os
+
+CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.1))
 
 DEBUG_CACHES = False
 
@@ -25,3 +29,56 @@ cache_counter = metrics.register_cache(
     lambda: {(name,): len(caches_by_name[name]) for name in caches_by_name.keys()},
     labels=["name"],
 )
+
+_string_cache = LruCache(int(5000 * CACHE_SIZE_FACTOR))
+caches_by_name["string_cache"] = _string_cache
+
+
+KNOWN_KEYS = {
+    key: key for key in
+    (
+        "auth_events",
+        "content",
+        "depth",
+        "event_id",
+        "hashes",
+        "origin",
+        "origin_server_ts",
+        "prev_events",
+        "room_id",
+        "sender",
+        "signatures",
+        "state_key",
+        "type",
+        "unsigned",
+        "user_id",
+    )
+}
+
+
+def intern_string(string):
+    """Takes a (potentially) unicode string and interns using custom cache
+    """
+    return _string_cache.setdefault(string, string)
+
+
+def intern_dict(dictionary):
+    """Takes a dictionary and interns well known keys and their values
+    """
+    return {
+        KNOWN_KEYS.get(key, key): _intern_known_values(key, value)
+        for key, value in dictionary.items()
+    }
+
+
+def _intern_known_values(key, value):
+    intern_str_keys = ("event_id", "room_id")
+    intern_unicode_keys = ("sender", "user_id", "type", "state_key")
+
+    if key in intern_str_keys:
+        return intern(value.encode('ascii'))
+
+    if key in intern_unicode_keys:
+        return intern_string(value)
+
+    return value