From baa94a31961aec31d6c1b2002bef7faf9ea557e3 Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Thu, 11 Jun 2020 12:09:37 -0400
Subject: [PATCH] Try setting the limit higher
---
nixos/modules/tahoe.nix | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/nixos/modules/tahoe.nix b/nixos/modules/tahoe.nix
index f1274534..0227ad9f 100644
--- a/nixos/modules/tahoe.nix
+++ b/nixos/modules/tahoe.nix
@@ -128,6 +128,38 @@ in
ExecStart = ''
${settings.package}/bin/tahoe run ${lib.escapeShellArg nodedir} -n -l- --pidfile=${lib.escapeShellArg pidfile}
'';
+
+ # The rlimit on number of open files controls how many
+ # connections a particular storage server can accept (factoring
+ # in the number of non-connection files the server needs open -
+ # eg for logging, reading and writing shares, etc).
+ #
+ # Once the maximum number of open files, as controlled by rlimit
+ # is reached, service suffers dramatically. New connections
+ # cannot be accepted. Shares cannot be read or written.
+ #
+ # The default limit on open files is 8192 (2^13). This could
+ # easily be raised. If it is raised to 2^16 then the rlimit is
+ # approximately equal to the limit imposed by TCP (which only
+ # has around 2^16 ports available per IP address). If we want
+ # each connection to also be able to read or write a share file,
+ # a limit of 2^15 would allow this. Then, we should scale the
+ # limit linearly with the number of IP addresses available. If
+ # the service can be reached on 2 IP addresses, allow twice as
+ # many files (2^15 * 2 = 2^16). If it can be reached on 3 IP
+ # addresses, (2^16 * 3). etc.
+ #
+ # Python also sometimes wants to open files as a side effect of
+ # other things going. For example, if there's a traceback, it
+ # opens the source files to read lines to put into the
+ # traceback. If random numbers are generated, /dev/urandom
+ # might be opened, etc. There is also some fixed overhead for
+ # listening ports and such. This currently doesn't factor into
+ # our choice but perhaps it could somehow.
+ #
+ # There is only one IPv4 address assigned to each host right
+ # now. So it makes sense to have the limit be 2^15 right now.
+ LimitNOFILE = 32768;
};
preStart = ''
if [ ! -d ${lib.escapeShellArg nodedir} ]; then
--
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