[Spread-users] View consistency

[Anders.Lindstrom at ubsw.com]

Hello Spread Users,

I have been having a bit of a look at Spread. I am very interested so far because I am looking for ordering guarantees. I know that the answer is probably implied by the documentation but the question I have is this: do the ordering guarantees extend to the membership messages? In particular, can I implement so-called virtual synchrony in Spread. I'm sure you know what view synchrony is but just to make my meaning clear, I'll tell you what <emph>I</emph> mean by virtual synchrony.

Group View: current list of members in the group
View change: change in membership of the group
Virtual synchrony (view consistency):
	1. there is a unique group view in any consistent state on which all members of the group agree
	2. if a message m is multicast in group view v before view change c, either no member in v that executes c
		ever receives m, or every member in v that executes c receives m before performing c

Basically this means that all non-failing members of a view receive exactly the same messages.

Sorry if this is repeat question. I couldn't find anything in the FAQ.

Regards,

Anders.

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