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Acquiring statistics by client process:

1. First-time request: client query planning node will send stats request to all server nodes. 
2. Getting response: 
1. If requested statistics are presented somewhere - node just return it to client
2. If statistics are presented on more than one server node - client will use the last one received.
3. If there are no statistics in all of them - client will choose random server node and require it to collect necessary statistics.
3. After getting statistics client will cache it and the server node, which sent it to renew statistics from the same node.

To request statistics following messages are used:

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