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From Александр Меньшиков <sharple...@gmail.com>
Subject Sort nodes in the ring in order to minimize the number of reconnections
Date Thu, 22 Dec 2016 10:59:29 GMT
Hello everyone,

As far as I know nodes are connected in a ring. For example if i have 6
nodes, with names A, B, C, D, E, and F they can connect in ring any
possible way: A-B-C-D-E-F-A, or A-F-B-E-C-D-A, etc. And if some node falls
out of topology neighboring nodes must reconnect. If nodes A,B and C
located in the same physical location, and D, E and F in another, and in
some time one physical location is not available in another, we can get
different number of reconnections. Best case scenario if we have ring like
A-B-CxD-E-FxA ('x' mean disconnect) -- then we get only one reconnect (C
reconnect to A or F reconnect to D -- depending on what part of the cluster
we leave alive). But now possible that case AxFxBxExCxDxA -- then we get a
lot of reconnections (A to B, B to C, C to A -- in general n/2
reconnections, where n -- number of nodes). And i think to add something to
ensure that we always have good sorting of nodes connections

Of course in real world we can have multiple levels of physical closeness.

In my opinion enough to add one parameter of 'int' to configuration (with
name like 'ExtraNodeOrder') and to change the method of comparison nodes so
that it first compared the 'ExtraNodeOrder', and then according to the old
criterion (as far as I know Ignite use topology version). So if some users
have multiple levels of physical closeness, he can use different bits. For
example use 16 high bits for DC number, and low 16 bits for racks.

Alternatively, we can add array of ‘int’ to configuration and compare nodes
in sequence from the zero element to the last.

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