[erlang-questions] monitor and failure detectors

Ulf Wiger <>
Thu Jun 3 10:24:58 CEST 2010

Monitors have no timeout. They trigger immediately when either
the process dies or the node of the process is disconnected.

Is it the latter event that you are referring to?
This can be configured using -kernel net_ticktime T, where
T is 60 seconds by default.

See http://www.erlang.org/doc/man/kernel_app.html

"net_ticktime = TickTime

Specifies the net_kernel tick time.
TickTime is given in seconds. Once every TickTime/4 second,
all connected nodes are ticked (if anything else has been
written to a node) and if nothing has been received from
another node within the last four (4) tick times that node
is considered to be down. This ensures that nodes which are
not responding, for reasons such as hardware errors, are
considered to be down.

The time T, in which a node that is not responding is
detected, is calculated as: MinT < T < MaxT where:

MinT = TickTime - TickTime / 4
MaxT = TickTime + TickTime / 4

TickTime is by default 60 (seconds). Thus, 45 < T < 75 seconds.

Note: All communicating nodes should have the same TickTime value specified.

Note: Normally, a terminating node is detected immediately."

Ulf W

Johan Montelius wrote:
> Some question on monitors:
> Is there a way to change the timeout of monitors to configure how eager 
> they will be to deliver a DOWN/noconnection message? Can this be changed 
> on a per monitor basis so one could monitor one process with a 0.1s 
> timeout and another with a 20s timeout?
> I guess it is the empd daemon that is responsible for tracking the state 
> of nodes on a host. If a node crashes a monitor will report 
> DOWN/noconnection. Could it be possible to have monitor generate a 
> DOWN/down or similar when/if it can be determined that the node (and 
> thus the process that we monitor) is actually down. The 
> DOWN/noconnection message leaves us in a state where we don't know it is 
> down or simply disconnected.
>   Johan

Ulf Wiger
CTO, Erlang Solutions Ltd, formerly Erlang Training & Consulting Ltd



Since January 1st 2010 Erlang Training and Consulting Ltd. has become ERLANG SOLUTIONS LTD.


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