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Multimaster assumptions
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Hi,
we are preparing to set up a more or less extensive test suite for
deltasync multimaster replication. Since the resolution of conflicts can
be arbitrary (as long as it is consistent), I would like to have a way
to compare the outcome to a single authoritative DIT, the "observer" below.
Preconditions:
- - all servers start with an identical database
- - each server has unique serverID assigned
A thought experiment:
There are N servers acting as delta-syncrepl providers, arbitrary
changes flow to some/all of the servers. The "replication topology" is
arbitrary and volatile, but from some moment on it is guaranteed that it
will stay strongly connected.
Let us add another server and call it an "observer". An observer acts as
a delta-syncrepl consumer to a (possibly changing) set of providers and
it never acts as a provider to any of the servers.
Given the above and barring any software bugs, I guess it is intended
that if all servers are running recent OpenLDAP the following should
hold for the experiment:
- - given that the flow of changes stops eventually, the (actual)
replication traffic will eventually stop too with all N servers holding
the exact same DIT
- - given the above, the (actual) replication traffic to the observer too
will stop eventually with the observer holding the exact same DIT as the
servers.
Are my expectations reasonable or should the experiment be restricted to
achieve that outcome of having a reliable observer node? How about
generalizing the experiment by allowing that some of the replication
connections be plain syncrepl?
Even though this experiment might be exaggerated, I still feel like
stating what is a tautology according to the design from my point of
view, but I would like to hear whether it is supposed to work even under
these conditions.
Cheers,
- --
Ondrej Kuznik
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