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net.dns: Add jitter to spread queries and reduce failures due to congestion

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This commit is contained in:
Matthew Wild 2020-06-25 15:29:49 +01:00
parent 3ff48b8386
commit d080fee323
1 changed files with 20 additions and 2 deletions
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22
net/dns.lua
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@ -72,6 +72,8 @@ local ztact = { -- public domain 20080404 lua@ztact.com
local get, set = ztact.get, ztact.set; local get, set = ztact.get, ztact.set;
local default_timeout = 15; local default_timeout = 15;
local default_jitter = 1;
local default_retry_jitter = 2;
-------------------------------------------------- module dns -------------------------------------------------- module dns
local _ENV = nil; local _ENV = nil;
@ -668,6 +670,8 @@ end
resolver.delays = { 1, 3 }; resolver.delays = { 1, 3 };
resolver.jitter = have_timer and default_jitter or nil;
resolver.retry_jitter = have_timer and default_retry_jitter or nil;
function resolver:addnameserver(address) -- - - - - - - - - - addnameserver function resolver:addnameserver(address) -- - - - - - - - - - addnameserver
self.server = self.server or {}; self.server = self.server or {};
@ -855,7 +859,7 @@ function resolver:query(qname, qtype, qclass) -- - - - - - - - - - -- query
packet = header..question, packet = header..question,
server = self.best_server, server = self.best_server,
delay = 1, delay = 1,
retry = socket.gettime() + self.delays[1] retry = socket.gettime() + self.delays[1];
qclass = qclass; qclass = qclass;
qtype = qtype; qtype = qtype;
qname = qname; qname = qname;
@ -869,7 +873,13 @@ function resolver:query(qname, qtype, qclass) -- - - - - - - - - - -- query
if not conn then if not conn then
return nil, err; return nil, err;
end end
conn:send (o.packet) if self.jitter then
timer.add_task(math.random()*self.jitter, function ()
conn:send(o.packet);
end);
else
conn:send(o.packet);
end
-- remember which coroutine wants the answer -- remember which coroutine wants the answer
if co then if co then
@ -920,8 +930,16 @@ function resolver:servfail(sock, err)
sock, err = self:getsocket(o.server); sock, err = self:getsocket(o.server);
if sock then if sock then
retried = true; retried = true;
if self.retry_jitter then
local delay = self.delays[((o.retries-1)%#self.delays)+1] + (math.random()*self.retry_jitter);
log("debug", "retry %d in %0.2fs", o.retries, delay);
timer.add_task(delay, function ()
sock:send(o.packet);
end);
else
log("debug", "retry %d (immediate)", o.retries); log("debug", "retry %d (immediate)", o.retries);
sock:send(o.packet); sock:send(o.packet);
end
end end
end end
if not retried then if not retried then