Change default `sync_response_cache_duration` (#13042)

changelog.d/13042.misc

+Set default `sync_response_cache_duration` to two minutes.

docker/complement/conf/workers-shared-extra.yaml.j2

@@ -103,4 +103,10 @@ server_notices:
   system_mxid_avatar_url: ""
   room_name: "Server Alert"
 
+
+# Disable sync cache so that initial `/sync` requests are up-to-date.
+caches:
+  sync_response_cache_duration: 0
+
+
 {% include "shared-orig.yaml.j2" %}

docs/usage/configuration/config_documentation.md

@@ -1137,8 +1137,8 @@ Caching can be configured through the following sub-options:
 * `sync_response_cache_duration`: Controls how long the results of a /sync request are
   cached for after a successful response is returned. A higher duration can help clients
   with intermittent connections, at the cost of higher memory usage.
-  By default, this is zero, which means that sync responses are not cached
-  at all.
+  A value of zero means that sync responses are not cached.
+  Defaults to 2m.
 * `cache_autotuning` and its sub-options `max_cache_memory_usage`, `target_cache_memory_usage`, and
    `min_cache_ttl` work in conjunction with each other to maintain a balance between cache memory 
    usage and cache entry availability. You must be using [jemalloc](https://github.com/matrix-org/synapse#help-synapse-is-slow-and-eats-all-my-ramcpu) 

synapse/config/cache.py

@@ -206,7 +206,7 @@ class CacheConfig(Config):
             self.cache_autotuning["min_cache_ttl"] = self.parse_duration(min_cache_ttl)
 
         self.sync_response_cache_duration = self.parse_duration(
-            cache_config.get("sync_response_cache_duration", 0)
+            cache_config.get("sync_response_cache_duration", "2m")
         )
 
     def resize_all_caches(self) -> None:

tests/utils.py

@@ -169,7 +169,7 @@ def default_config(name, parse=False):
         # disable user directory updates, because they get done in the
         # background, which upsets the test runner.
         "update_user_directory": False,
-        "caches": {"global_factor": 1},
+        "caches": {"global_factor": 1, "sync_response_cache_duration": 0},
         "listeners": [{"port": 0, "type": "http"}],
     }