Hi Ben,
On 03/30/2016 06:13 PM, Ben Pfaff wrote:
I understand the technical differences between the approaches. My
question is whether high availability is your actual goal. If it is,
then it probably does not make sense to have multiple implementations.
If you are trying to accomplish something else, then it could be that
there is something complementary about the two implementations.
I believe the two approaches are complementary.
Like I said, the proposed patch aims at having a stand by database
available, but since there's no proxy or anything like that, if the
active database goes down, clients would have to reconnect. Ideally,
after failover, the stand-by database becomes the active and clients can
reuse the same connection parameters, but a reconnection must happen. If
someone is interested in filling that gap, haproxy is an option, but I
have not yet tested it. Same thing applies to a Raft-based solution.
What you are doing with Raft is complementary in the sense that you can
have six database servers, expose three of them to the clients and the
other three become stand-bys for the three active ones. If any of the
three actives go down, the corresponding stand-by steps up. With Raft,
with 6 active databases, you can loose 2 (4 are needed for consensus).
With this approach you only have 3 databases in service, but you can
loose all three. Obviously you can come up with other topologies like
3+1, or 5+1, etc. The proposed patch is the "+" part in that design.
Marcelo
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