Reload cache factors from disk on SIGHUP (#12673)

2 files changed, 23 insertions, 0 deletions

diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index a803b8261d..e7b57f5a0b 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -730,6 +730,12 @@ retention:
 # A cache 'factor' is a multiplier that can be applied to each of
 # Synapse's caches in order to increase or decrease the maximum
 # number of entries that can be stored.
+#
+# The configuration for cache factors (caches.global_factor and
+# caches.per_cache_factors) can be reloaded while the application is running,
+# by sending a SIGHUP signal to the Synapse process. Changes to other parts of
+# the caching config will NOT be applied after a SIGHUP is received; a restart
+# is necessary.
 
 # The number of events to cache in memory. Not affected by
 # caches.global_factor.
diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md
index 21dad0ac41..f292b94fb0 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -1130,6 +1130,23 @@ caches:
   expire_caches: false
   sync_response_cache_duration: 2m
 ```
+
+### Reloading cache factors
+
+The cache factors (i.e. `caches.global_factor` and `caches.per_cache_factors`)  may be reloaded at any time by sending a
+[`SIGHUP`](https://en.wikipedia.org/wiki/SIGHUP) signal to Synapse using e.g.
+
+```commandline
+kill -HUP [PID_OF_SYNAPSE_PROCESS]
+```
+
+If you are running multiple workers, you must individually update the worker 
+config file and send this signal to each worker process.
+
+If you're using the [example systemd service](https://github.com/matrix-org/synapse/blob/develop/contrib/systemd/matrix-synapse.service)
+file in Synapse's `contrib` directory, you can send a `SIGHUP` signal by using
+`systemctl reload matrix-synapse`.
+
 ---
 ## Database ##
 Config options related to database settings.