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From "ilya.kasnacheev" <ilya.kasnach...@gmail.com>
Subject Re: Impact of connectionsPerNode and pairedConnection
Date Mon, 18 Dec 2017 16:28:22 GMT
Hello!

Paired connections are known to improve performance and even cluster
stability. I guess they're not ON by default for the sake of backward
compatibility and because they're somewhat less battle-tested than
non-paired connections.

With regards of memory consumption, they should not increase consumption per
se. One thing I can think of - more throughput, longer queues, increased
parallelism leading to increased amount of temporary objects at any given
moment of time.  If you could compare memory dump analysis class histogram
before and after setting change with the same workload, we could discuss the
differences.

You can learn more about these settings from the javadoc of 
https://ignite.apache.org/releases/latest/javadoc/org/apache/ignite/spi/communication/tcp/TcpCommunicationSpi.html

When you have only one unpaired connections, operations wishing to
communicate with another node need to wait until this connection becomes
available. When you have multiple connections, they only need to wait for
the next available one. Usually it is not a problem, that's why one unpaired
connection is the default. I guess you've found use case where this becomes
constraining factor. That's what advanced settings are for - corner cases.

In 2.3, there's better detection of failed connections when paired
connections are used. This makes me suspect you may have network problems
with packets delayed or lost, and connections sometime break. In this case,
when you have 5 connections both ways and not just 1, not all the work is
stalled but merely one thread when waiting for packet retransmit. Have you
solve the network problems, you may probably go with 1 or 2 connections
instead of five.

Regards,



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