Various improvements to the docs (#7899)

3 files changed, 25 insertions, 14 deletions

diff --git a/debian/changelog b/debian/changelog
index 3825603ae4..99165b61fd 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,13 @@
+matrix-synapse-py3 (1.xx.0) stable; urgency=medium
+
+  [ Synapse Packaging team ]
+  * New synapse release 1.xx.0.
+
+  [ Aaron Raimist ]
+  * Fix outdated documentation for SYNAPSE_CACHE_FACTOR
+
+ -- Synapse Packaging team <packages@matrix.org>  XXXXX
+
 matrix-synapse-py3 (1.17.0) stable; urgency=medium
 
   * New synapse release 1.17.0.
diff --git a/debian/matrix-synapse.default b/debian/matrix-synapse.default
index 65dc2f33d8..f402d73bbf 100644
--- a/debian/matrix-synapse.default
+++ b/debian/matrix-synapse.default
@@ -1,2 +1,2 @@
 # Specify environment variables used when running Synapse
-# SYNAPSE_CACHE_FACTOR=1 (default)
+# SYNAPSE_CACHE_FACTOR=0.5 (default)
diff --git a/debian/synctl.ronn b/debian/synctl.ronn
index a73c832f62..1bad6094f3 100644
--- a/debian/synctl.ronn
+++ b/debian/synctl.ronn
@@ -46,19 +46,20 @@ Configuration file may be generated as follows:
 ## ENVIRONMENT
 
   * `SYNAPSE_CACHE_FACTOR`:
-    Synapse's architecture is quite RAM hungry currently - a lot of
-    recent room data and metadata is deliberately cached in RAM in
-    order to speed up common requests.  This will be improved in
-    future, but for now the easiest way to either reduce the RAM usage
-    (at the risk of slowing things down) is to set the
-    SYNAPSE_CACHE_FACTOR environment variable. Roughly speaking, a
-    SYNAPSE_CACHE_FACTOR of 1.0 will max out at around 3-4GB of
-    resident memory - this is what we currently run the matrix.org
-    on. The default setting is currently 0.1, which is probably around
-    a ~700MB footprint. You can dial it down further to 0.02 if
-    desired, which targets roughly ~512MB. Conversely you can dial it
-    up if you need performance for lots of users and have a box with a
-    lot of RAM.
+    Synapse's architecture is quite RAM hungry currently - we deliberately
+    cache a lot of recent room data and metadata in RAM in order to speed up
+    common requests. We'll improve this in the future, but for now the easiest
+    way to either reduce the RAM usage (at the risk of slowing things down)
+    is to set the almost-undocumented ``SYNAPSE_CACHE_FACTOR`` environment
+    variable. The default is 0.5, which can be decreased to reduce RAM usage
+    in memory constrained enviroments, or increased if performance starts to
+    degrade.
+
+    However, degraded performance due to a low cache factor, common on
+    machines with slow disks, often leads to explosions in memory use due
+    backlogged requests. In this case, reducing the cache factor will make
+    things worse. Instead, try increasing it drastically. 2.0 is a good
+    starting value.
 
 ## COPYRIGHT