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From John Wilson <sami.hailu...@gmail.com>
Subject Re: A quick question on cluster topology and partitions?
Date Tue, 03 Jul 2018 00:20:18 GMT
Regarding 1. I'm referring to the documentation here,
https://apacheignite.readme.io/docs/topology-validation, which states
"*Topology
validator is used to verify that cluster topology is valid for further
cache operations*." and "*If topology validator is not configured, then the
cluster topology is always considered to be valid.*"

Thanks,

On Mon, Jul 2, 2018 at 4:21 PM, Dmitriy Setrakyan <dsetrakyan@apache.org>
wrote:

> On Mon, Jul 2, 2018 at 4:03 PM, John Wilson <sami.hailu.15@gmail.com>
> wrote:
>
> > Hi,
> >
> >
> >    1. What exactly is a cluster topology? What makes a cluster topology
> >    invalid for further cache operations?
> >
>
> Cluster topology is a set of Ignite nodes in the cluster. I do not think a
> cluster topology could be invalid on its own. Perhaps you are asking about
> a situation when after a certain number of node failures/stops we can be in
> a situation where all primary and backup copies become inaccessible. In
> that case, the cluster should enter a read-only state for the lost
> partitions.
>
>
> >    2.  Why do we have the concept of partitions in Ignite? Why don't we
> >    have a key-to-node mapping rather than a key-to-partition and a
> >    partition-to-node mapping?
> >
>
> Main reason is because there is a finite number of partitions and there is
> an infinite number of keys. Whenever ignite topology changes, Ignite must
> rebalance data to the new nodes (or to the existing nodes). In this case,
> Ignite needs to know when a certain partition is moved to another node. If
> there were no partitions, then it would be impossible to tell when to
> finish the rebalancing process.
>
> D.
>

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