[zeromq-dev] Heartbeating using TCP keepalives

[Pieter Hintjens]

Seconds is fine for this case but surprising overall since all other
durations in the API are in msec.

I'm not sure what you mean about backwards compatibility.

On Thu, Jan 2, 2014 at 7:55 PM, Alex Grönholm <alex.gronholm at nextday.fi> wrote:
> 02.01.2014 15:59, Pieter Hintjens kirjoitti:
>> It makes sense, and I'd try this; the timeout should be in msec, to be
>> consistent with other duration arguments. You can take any of the
>> existing socket options like ZMQ_SNDBUF as a template, and make a pull
>> request.
> Wouldn't it be enough to document that the values are expressed in
> seconds and not ms?
> Who needs sub-second accuracy with keepalives?
> Besides, converting the values on non-Windows systems would break
> backwards compatibility.
> Are you fine with that? This definitely should not be done in a micro
> release.
>>
>> On Mon, Dec 30, 2013 at 11:29 PM, Alex Grönholm
>> <alex.gronholm at nextday.fi> wrote:
>>> This isn't directly related to ZeroMQ, but it is somewhat relevant now given
>>> A) the addition of the (yet unimplemented) heartbeating feature in ZMTP/3.0
>>> and B) the Windows TCP keepalive parameters fix I committed recently.
>>> The question is: has someone here used TCP keepalives as a substitute for
>>> application level heartbeating? Given the operating model of ZeroMQ, using
>>> TCP keepalives for this purpose would transparently shield the user from
>>> stale connections. Are there any downsides to this?
>>> TCP keepalives, when turned on, use a 2 hour interval by default (this is a
>>> de facto standard). This makes them impractical unless the values are
>>> adjusted.
>>> I've done some research on that. From what I've gathered, it seems that
>>> setting TCP keepalive parameters on a per-socket level is supported at least
>>> on the following operating systems:
>>>
>>> Linux
>>> FreeBSD
>>> Windows (since Windows 2000; set only, read not supported; number of
>>> keepalive probes is fixed on 10; must be set before connecting; values in
>>> milliseconds, not seconds)
>>> Mac OS X (since Mountain Lion)
>>> AIX
>>> Solaris (values in milliseconds, not seconds)
>>>
>>> It seems that both iOS and Android support sending TCP keepalives, but
>>> setting keepalive parameters is not supported.
>>> Note that the Windows TCP keepalive parameters patch takes the time
>>> intervals in seconds and multiplies by 1000 on Windows for cross platform
>>> compatibility. There is no similar fix for Solaris yet so Solaris users need
>>> to do it on the application level for now.
>>>
>>> Setting the keepalive idle and retransmission delay to values like 10 and 5
>>> seconds would make a lot of sense to me. If the peer fails to respond to the
>>> probes, zmq will just see a disconnection.
>>>
>>>
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>>>
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