On 05/22/2012 09:48 AM, Anand Avati wrote:
I've tried to understand how AFR works and, in some way,
some of the ideas have been taken from it. However it is
very complex and a lot of changes have been carried out in
the master branch over the latest months. It's hard for me
to follow them while actively working on my translator.
Nevertheless, the main reason to take a separate path was
that AFR is strongly bound to replication (at least from
what I saw when I analyzed it more deeply. Maybe things have
changed now, but haven't had time to review them).
Have you reviewed the proactive self-heal daemon (+
changelog indexing translator) which is a potential functional
replacement for what you might be attempting?
Avati
I must admit that I've read something about it but I haven't had
time to explore it in detail.
If I understand it correctly, the self-heal daemon works as a client
process but can be executed on server nodes. I suppose that multiple
self-heal daemons can be running on different nodes. Then, each
daemon detects invalid files (not sure exactly how) and replicates
the changes from one good node to the bad nodes.
The problem is that in the translator I'm working on, the
information is dispersed among multiple nodes, so there isn't a
single server node that contains the whole data. To repair a node,
data must be read from at least two other nodes (it depends on
configuration). From what I've read from AFR and the self-healing
daemon, it's not straightforward to adapt them to this mechanism
because they would need to know a subset of nodes with consistent
data, not only one. Each daemon would have to contact all other
nodes, read data from each one, determine which ones are valid,
rebuild the data and send it to the bad nodes. This means that the
daemon will have to be as complex as the clients.
My impression (but I may be wrong) is that AFR and the self-healing
daemon are closely bound to the replication schema, so it is very
hard to try to use them for other purposes. The healing translator
I'm writing tries to offer generic server side helpers for the
healing process, but it is the client side who really manages the
healing operation (though heavily simplified) and could use it to
replicate data, to disperse data, or some other schema.
Xavi
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