ianluites / data_daemon Goto Github PK

While the use DataDaemon macro is very handy, it limits any time of run-time configurability, see also #2

My suggestion is being able to configure DataDaemon when it is included in the parent app supervisor tree, example:

# In your application code
defmodule Sample.DataDog do
  @moduledoc ~S"My DataDog reporter."
  use DataDaemon,
    otp_app: :my_app,
    extensions: [:datadog]
end

# In parent app supervisor
Sample.DataDog.start_link(url: "statsd+udp://localhost:8125")

Any parameter passed to start_link overrides any set in the application config file.

I'd like to take a stab at this, but as it'll break the existing API I'll wait for your go-ahead.

We've been noticing an idle 25% CPU scheduler usage in staging, when DataDaemon is active.

Observer shows the process timer_server using most of the CPU time, which is the gen_server that powers the erlang :timer module. Killing this process restores a 0% idle CPU usage.

There's a call to :timer.apply_after in

(<0.22660.1888>) call timer:apply_after(600000,'Elixir.DataDaemon.Hound','host_check!',[<0.22660.1888>,"datadog_agent",8125,{10,0,7,27},ttl])
(<0.23963.1888>) call timer:apply_after(600000,'Elixir.DataDaemon.Hound','host_check!',[<0.23963.1888>,"datadog_agent",8125,{10,0,7,27},ttl])
(<0.23981.1888>) call timer:apply_after(600000,'Elixir.DataDaemon.Hound','host_check!',[<0.23981.1888>,"datadog_agent",8125,{10,0,7,27},ttl])
(<0.22771.1888>) call timer:apply_after(600000,'Elixir.DataDaemon.Hound','host_check!',[<0.22771.1888>,"datadog_agent",8125,{10,0,7,27},ttl])
(<0.23878.1888>) call timer:apply_after(600000,'Elixir.DataDaemon.Hound','host_check!',[<0.23878.1888>,"datadog_agent",8125,{10,0,7,27},ttl])
etc...

All of these are executed at the same time.

I seem to understand the logic between host_check!, but I'm not sure it's worth 25% of the CPU cycles, and it should probably default to disabled TTL refreshing, unless manually configured to do so.

Quoting from http://erlang.org/doc/efficiency_guide/commoncaveats.html

Creating timers using erlang:send_after/3 and erlang:start_timer/3 , is much more efficient than using the timers provided by the timer module in STDLIB. The timer module uses a separate process to manage the timers. That process can easily become overloaded if many processes create and cancel timers frequently (especially when using the SMP emulator).

Though undocumented, it's possible to set some default tags by calling use DataDaemon, tags: [foo: "bar"], but they are set at compile time, and it's currently impossible to have a different set of default tags at runtime — for example, tags derived from environment variables.