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diff --git a/README.rst b/README.rst index 35141ac71b..12f0c0c51a 100644 --- a/README.rst +++ b/README.rst @@ -528,6 +528,30 @@ fix try re-installing from PyPI or directly from # Install from github pip install --user https://github.com/pyca/pynacl/tarball/master +Running out of File Handles +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If synapse runs out of filehandles, it typically fails badly - live-locking +at 100% CPU, and/or failing to accept new TCP connections (blocking the +connecting client). Matrix currently can legitimately use a lot of file handles, +thanks to busy rooms like #matrix:matrix.org containing hundreds of participating +servers. The first time a server talks in a room it will try to connect +simultaneously to all participating servers, which could exhaust the available +file descriptors between DNS queries & HTTPS sockets, especially if DNS is slow +to respond. (We need to improve the routing algorithm used to be better than +full mesh, but as of June 2017 this hasn't happened yet). + +If you hit this failure mode, we recommend increasing the maximum number of +open file handles to be at least 4096 (assuming a default of 1024 or 256). +This is typically done by editing ``/etc/security/limits.conf`` + +Separately, Synapse may leak file handles if inbound HTTP requests get stuck +during processing - e.g. blocked behind a lock or talking to a remote server etc. +This is best diagnosed by matching up the 'Received request' and 'Processed request' +log lines and looking for any 'Processed request' lines which take more than +a few seconds to execute. Please let us know at #matrix-dev:matrix.org if +you see this failure mode so we can help debug it, however. + ArchLinux ~~~~~~~~~ |