[Spread-users] Spread 4

[Theo Schlossnagle]

Yair Amir wrote:

> The new version has considerable changes from Spread 3, changing
> the way virtual synchrony sets are reported in membership messages.
> This is done for a good reason - to support a stronger semantics, that 
> comes
> for free, for membership VS sets (instead of who-came-with-us, we can now
> know who-came-with-whom, which happens to be very useful in the 
> context of
> fast synchronization as well as for some security algorithms). Of 
> course, the
> [snip]
> - Ability to dynamically add and remove machines from the 
> configuration, with
>   deep optimization for the common cases everyone is screaming about 
> for a few
>   years now. We at Spread Concepts experimented with a few different 
> solutions
> [snip]
> - Inclusion of the Flush layer (virtual synchrony) as an integral part 
> of Spread.
> [snip]

Many congratulations on the up and coming release of Spread 4.  It is 
very exciting!

The who-came-with-whom change sounds nice for optimizing replication 
systems with commutative semantics.  It will require a lot less 
application-level coordination.  Very excellent.

I'd imagine the robustness being discussed isn't simply some patches 
here and there.  Our robustness checks (just inteneral to software, not 
including byzantine network nodes) consist of automated test suites that 
excercise the systems with clear code coverage assessments -- making 
sure every line of code (every possible code path) is executed during 
when performing the test suite.  This can be a challenge for a product 
like Spread (being distributed), but excellent coverage is still 
possible.  On the network side of things, byzantine nodes are the common 
focus, but Spread 3, for example, can have some catastrophic failures 
from simple node misconfiguration.  While I know that a protocol 
engineer would consider a single node with a bad configuration as 
byzantine, a deployment engineer would not -- they'd consider it a 
misconfiguration and expect it reported as such  :-)

Best regards,

Theo