|
|
@@ -340,8 +340,11 @@ log lines and looking for any 'Processed request' lines which take more than
|
|
|
a few seconds to execute. Please let us know at #synapse:matrix.org if
|
|
|
you see this failure mode so we can help debug it, however.
|
|
|
|
|
|
-Help!! Synapse eats all my RAM!
|
|
|
--------------------------------
|
|
|
+Help!! Synapse is slow and eats all my RAM/CPU!
|
|
|
+===============================================
|
|
|
+
|
|
|
+First, ensure you are running the latest version of Synapse, using Python 3
|
|
|
+with a PostgreSQL database.
|
|
|
|
|
|
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
|
|
|
@@ -352,14 +355,29 @@ 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.
|
|
|
+
|
|
|
Using `libjemalloc <http://jemalloc.net/>`_ can also yield a significant
|
|
|
-improvement in overall amount, and especially in terms of giving back RAM
|
|
|
-to the OS. To use it, the library must simply be put in the LD_PRELOAD
|
|
|
-environment variable when launching Synapse. On Debian, this can be done
|
|
|
-by installing the ``libjemalloc1`` package and adding this line to
|
|
|
-``/etc/default/matrix-synapse``::
|
|
|
+improvement in overall memory use, and especially in terms of giving back
|
|
|
+RAM to the OS. To use it, the library must simply be put in the
|
|
|
+LD_PRELOAD environment variable when launching Synapse. On Debian, this
|
|
|
+can be done by installing the ``libjemalloc1`` package and adding this
|
|
|
+line to ``/etc/default/matrix-synapse``::
|
|
|
|
|
|
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.1
|
|
|
|
|
|
This can make a significant difference on Python 2.7 - it's unclear how
|
|
|
much of an improvement it provides on Python 3.x.
|
|
|
+
|
|
|
+If you're encountering high CPU use by the Synapse process itself, you
|
|
|
+may be affected by a bug with presence tracking that leads to a
|
|
|
+massive excess of outgoing federation requests (see `discussion
|
|
|
+<https://github.com/matrix-org/synapse/issues/3971>`_). If metrics
|
|
|
+indicate that your server is also issuing far more outgoing federation
|
|
|
+requests than can be accounted for by your users' activity, this is a
|
|
|
+likely cause. The misbehavior can be worked around by setting
|
|
|
+``use_presence: false`` in the Synapse config file.
|
Benjamin Saunders