Various improvements to the docs (#7899)
1 files changed, 14 insertions, 13 deletions
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
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