[erlang-questions] High lock contention on dist_tables

[Lukas Larsson]

Hello Brian,

Just letting you know that I have just merged a fix which changes the
rwlock I mentioned before to an rlock. This should reduce the contention
which you are seeing if it was caused by many calls to erlang:nodes().

Lukas


On Tue, Apr 23, 2013 at 9:01 PM, Scott Lystig Fritchie <
fritchie@REDACTED> wrote:

> Brian Picciano <mediocregopher@REDACTED> wrote:
>
> bp> We have a pool of 3 erlang nodes, all on different servers. Every
> bp> afternoon, without fail, we start seeing lots of messages between
> bp> the nodes start having really high latency, on the order of tens of
> bp> seconds. [...]
>
> Brian, it's probably worthwhile to continue chasing the 'lcnt' avenue
> as you've been corresponding with Lukas...
>
> ... but at the same time, I also wonder about "tens of seconds".  My gut
> says that such delays would require some amazingly high lock contention
> rates.  Something that can cause such messaging delays much more easily
> is network congestion/packet loss that triggers TCP slow start.  Many
> Linux kernels have the RTO_min value at one second, which is the amount
> of time to wait before entering slow start state.
>
> If network packet loss is a problem, this blog posting can explain one
> reason why it's happening:
> http://www.snookles.com/slf-blog/2012/01/05/tcp-incast-what-is-it/
>
> -Scott
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