PingPeriod

[roger peppe]

I just noticed this email. I don't think it's a problem - there's
just an unfortunate naming coincidence. The Pinger that
the CL is talking about is an API server nullop - we're just
checking to make sure the API is alive by sending a request
and receiving the response.

It's totally unrelated to the Pinger defined in state/presence,
unless I'm missing something crucial here.

On 3 July 2013 07:33, John Arbash Meinel <john at arbash-meinel.com> wrote:
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> wrt this change: https://codereview.appspot.com/10620043/patch/11001/8003
>
> I came to this late, but I wanted to mention that I think this will
> break the logic in status as to what machines are alive and what
> machines are not.
>
> Specifically, if you look at state/presence/presence.go the
> Watcher.sync() loop looks for beings that have been active in either
> the current slot, or the previous slot.
>
> The slot period is defined as 30s. So agents must produce a ping
> within that time, or we will perceive them as missing/dead/etc.
>
> Consider the case where we just rolled into a new period, so the
> previous period started 31s before.
>
> That means that on average ~half of the pingers would be seen as
> inactive. (Not active in current, didn't ping in last).
>
> I would probably rather see PingPeriod == slot period. So every 30s.
> On average, every pinger hits every slot, and occasionally we will
> skip a slot, or hit a slot twice.
>
> Alternatively we can back off the presence code, and have it check
> more slots.
>
> Also, in the current system, it doesn't actually hammer the servers
> because it has:
>
> if lastSlot == slot {
>   return nil
> }
>
> So it only ever pings 1 time per slot anyway.
>
> I realize in the API case, we are likely (certainly in my design) to
> compute the slot in the API server, so it would add some load to the
> API server to see and then discard those 5s pings.
>
> Thoughts?
>
> John
> =:->
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