Gordon Messmer wrote:
Chris St. Pierre wrote:
You'll want to set up two-way replication agreements between each pair
of hosts in your setup. So if you had A, B, C, and D, you'd set up
agreements between A-B, A-C, A-D, B-C, B-D, and C-D.
The documentation contradicts you. Look at the second figure in the
"Multi-Master Replication" section of the admin manual (hard to see),
and the section "Configuring 4-Way Multi-Master Replication" several
pages below it:
http://www.redhat.com/docs/manuals/dir-server/ag/7.1/replicat.html#1101818
The admin manual suggests a ring topology (and two agreements per set of
peers) for multi-master agreements. You should have agreements between
A->B, A->D, B->A, B->C, C->B, C->D, D->C, and D->A.
Ring-topology survives 1 server failure, but not two. You need to
understand your high-availability requirements to decide which is right
for you.
Full-mesh replication supports 2 servers failing at the same time, but
increases replication traffic.
Mininum level of agreements for 4-way MMR:
1 <-> 2
1 <-> 3
2 <-> 4
Maximum level of agreements (full-mesh) for 4-way MMR (each machine
replicates to 3 targets):
1 <-> 2
1 <-> 3
1 <-> 4
2 <-> 3
2 <-> 4
3 <-> 4
Again, it's much easier to visualize when you draw numbered boxes on
paper and connect the dots :-)
The systems I design require high-availability for writes, so I use
full-mesh MMR.
--
mike
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