[erlang-questions] [ANN] ActorDB a distributed SQL database (Sergej Jurecko)

Fred Hebert mononcqc@REDACTED
Fri Jan 24 17:33:32 CET 2014

I'm curious about a few things:

- You mention using ACID for transactions, but later mention "The master
  does periodic rebroadcasts of state. Eventually it will correct
  itself. But it had bad data for X seconds"

  This points towards an eventually consistent solution, not a fully
  consistent one.

- There is, during your leader election (picking local max) and many
  times around the text: "A successful 2 phase commit means a majority
  of nodes."

  This sounds like a majority-based consensus, but the 2PC algorithm
  usually waits for *all* participants to have agreed. Unless you're
  adding majority-reads as a constraints, it sounds like you're going to
  be breaking ACID in the first place, and that you're not actually
  using 2PC, but a quorum-based consensus algorithm.

- It's unclear how 'majority' is determined. Is it a majority of all the
  nodes *expected* in the cluster, or a majority of the nodes
  *currently* in the cluster? How does this deal with netsplits?

- No mention of timeout. Do you have a threshold under which a master
  gets de-elected for taking too long to respond? Is there an assumption
  here about timeouts vs. failures and how to tell them apart? Under
  such a scenario, how do two nodes who think of each other as masters
  detect the case and resolve it?

- How do these mechanism keep working following a netsplit during a
  multi-shard transaction?

- When you redirect requests, are you doing the redirection as a proxy,
  or asking to retry directly? In the former case, what happens if the
  proxy node dies, but not the master actually doing the request? Or
  vice-versa, what if the client dies, but not the proxy node?

- What happens to requests being sent during a shard migration that
  hasn't yet completed?

There's probably more to ask, but yeah. Distributed systems are fun and


On 01/24, Sergej Jurecko wrote:
> hello,
> We've put up a documentation page with more info. 
> http://www.actordb.com/docs.html
> Hopefully it answers more questions than it raises. If not fire away.
> Sergej
> On Jan 22, 2014, at 10:19 PM, Valery Meleshkin wrote:
> > Hi Sergej,
> > 
> > Which algorithms were used to build it? How its architecture looks like? How testing process looks like?
> > Specifically I’m interested in the details of replication, inter-actor transaction coordination, replica placement and membership service (e.g. raft/paxos/2pc/ 2pc over paxos ensembles/…).
> > 
> > -- 
> > Sincerely,
> > (Mr.) Valery Meleshkin
> > 
> > 
> > 
> > _______________________________________________
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