[squeak-dev] trunk process resilience

Frank Shearar frank.shearar at gmail.com
Thu Nov 7 21:33:33 UTC 2013


On 7 November 2013 21:07, Chris Muller <ma.chris.m at gmail.com> wrote:
> Lately we've had some problems with the SqueakSource server that supports
> our vital trunk process.  Ken and I burned several hours on it this week.
> The experience has caused me to consider an idea for improved continuity of
> our trunk repository.
>
> Very simply, it's a second running copy of trunk (and inbox, et al).  Each
> instance keeps itself up to date from the other.  If one goes down, the
> other can be pointed to for updates AND commits to minimize disruption.
>
> Right now, we actually already have two trunks.  Now, I'm pleased to
> announce that new-trunk running on box4.squeak.org is now a *full-copy* of
> old-trunk on box2.  (Before it was only trunk, now it includes Inbox, Etoys,
> etc.).  Using newer and better code and VM and also Magma, this copy of
> trunk was originally brought up simply to provide MC method history directly
> into the IDE, but now I can see its role being to improve trunk process
> stability so that community development can be continuous until it
> eventually becomes the defacto trunk (e.g., running source.squeak.org).
>
> There are other side-benefits too, like the ability to move or upgrade the
> trunk without a service interruption.  We are assured to be ready to move to
> a different server on a moments notice, e.g., break the link with Hetzner.
>
> So, I guess I'm proposing that we have some elements in the image "aware" of
> a second trunk.  But before wrangling out exactly what form that awareness
> would take, what do you think so far?

I think before any person pitches in with any suggestion, that person
should go read up on handling state in a distributed system. (Because
having a second copy in a kind've active-active replication thing is
exactly a distributed system.) It is _not_easy_. (And "Never go to sea
with two chronometers; take one or three".) Here's a good starting
point: http://aphyr.com/posts/281-call-me-maybe-carly-rae-jepsen-and-the-perils-of-network-partitions

frank


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