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From Dmitriy Setrakyan <dsetrak...@apache.org>
Subject Re: A quick question on cluster topology and partitions?
Date Mon, 02 Jul 2018 23:21:42 GMT
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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