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From Eduard Shangareev <eduard.shangar...@gmail.com>
Subject New definition for affinity node (issues with baseline)
Date Tue, 24 Apr 2018 14:46:30 GMT
Hi, Igniters,

I want to raise a topic about our affinity node definition.

After adding baseline (affinity) topology (BL(A)T) things start being
complicated.

Plenty of bugs appears:

IGNITE-8173
ignite.getOrCreateCache(cacheConfig).iterator() method works incorrect for
replicated cache in case if some data node isn't in baseline

IGNITE-7628
SqlQuery hangs indefinitely with additional not registered in baseline node.

It's because everything relies on concept "affinity node".
And until now it was as simple as a server node which passes node filter.
Other words any server node which is not filtered out by node filter.

But node which is not in BL(A)T and which passes node filter would be
treated as affinity node. And it's definitely wrong. At least, it is a
source of many bugs (I believe there are much more than those 2 which I
already have mentioned).

It's clear that this definition should be changed.
Let's start with a new definition of "Affinity topology". Affinity topology
is a set of nodes which potentially could keep data.

If we use knowledge about the current realization we can say that 1. for
in-memory cache groups it would be all server nodes;
2. for persistent cache groups it would be BL(A)T.

I will further use Dynamic Affinity Topology or DAT for 1 (in-memory cache
groups) and Static Affinity Topology or SAT instead BL(A)T, or 2nd point.

Denote node filter as f(X), where X is affinity topology.

Then we can say that node A is affinity node if
A ∈ AT', where AT' = f(AT), where AT is DAT or SAT.

It worth to mention that AT' should be used to pass to affinity function of
cache groups.
Also, AT and AT' could change during the time (BL(A)T changes or node
joins/disconnections).

And I don't like fact that usage of DAT or SAT relies on persistence
settings (Should we make it configurable per cache group?).

Ok, I have created a ticket to implement this changes and will start
working on it.
https://issues.apache.org/jira/browse/IGNITE-8380 (Affinity node
calculation doesn't take into account BLT).

Also, I want to use these definitions (Affinity Topology, Affinity Node,
DAT, SAT) in documentation and java docs.

Maybe, we also should consider replacing BL(A)T with SAT.

Thank you for your attention.

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