Network Partition

[Rohit Manohar]

Hello

I wanted to know how terrastore (terracotta rather) will behave in
case of network partioning between the active and passive master.
Also, once network connectivity has been re-established, what will be
the behaviour.

Regards
Rohit Manohar

PS: I wanted to +1 Terrastore, too bad there isn't such an option.

[Raffaele Sena]

Terracotta is quite sensitive to network glitches and the behavior depends on how you configure the cluster.

The standard behavior is that a client that loses connectivity for more than a specific (configurable) time is rejected by the TC server until you restart the client.

The other common problem is the "split brain" problem, where the active and passive Terracotta server can't ping each other because of connectivity issues and both elect themselves as the "active" server (then when the network problem is solved one of the server will realize the "split brain" state and kill itself, and again you'll have to restart it). This also is solvable by correctly tuning the various timeouts in the Terracotta configuration (how often the servers ping each other, how long clients should wait before trying to connect to the passive server and so on).

You can read more here (you'll need to register first) :

http://www.terracotta.org/documentation/high-availability.html

-- Raffaele

[Sergio Bossa]

On Thu, Jul 7, 2011 at 5:55 PM, Raffaele Sena <raf...@gmail.com> wrote:

> The other common problem is the "split brain" problem, where the active and
> passive Terracotta server can't ping each other because
> of connectivity issues and both elect themselves as the "active" server
> (then when the network problem is solved one of the server will realize the
> "split brain" state and kill itself, and again you'll have to restart it).

That's not quite correct: the "split brain" problem in Terracotta only
happens when the two masters get an equal number of clients (servers
in Terrastore parlance) after the split, and in such a case the master
will "notify" the problem and wait for human action; otherwise the
master with the majority of connected clients will stay alive, and the
other will shut down.
Let me give an example: given an active/passive topology with 10
clients, if you get a partition and 7 clients connect to master 1 and
3 clients to master 2, master 1 will stay active and master 2 will
shut down.

Hope that clarifies.
Cheers,

Sergio B.

--
Sergio Bossa
http://www.linkedin.com/in/sergiob