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From Brian Macker <brianmackerda...@hotmail.com>
Subject Question on non-quorum reads of untimely data
Date Mon, 26 Nov 2018 15:58:44 GMT
I have researched and could find not clear answer for this situation in the documentation,
tutorials, ornon other sites.

Hypothetical: I need to read configuration information from a zookeeper server.  Stale data
is acceptable. Untimely data is acceptable.

However network failures occurred.  The client is only able to connect to a zookeeper server
not currently a part of any quorum, due to network problems.  Assume that all the servers
accessible from the client have in fact already detected disconnection from leader and inablity
to elect a new leader. [Each acessible server is part of a minority (non-quorum) of the entire
ensemble].

Also assume that the consistency rule on timeliness has been exceeded, and all accessible
minority servers know this.

Question: Can the client read untimely (and potentially stale) data out of one of the accessible
untimely minority server nodes, or does it recieve some error result instead?

I am concerned that a Spring Boot Cloud Config set up to use Zookeeper could prevent an application
from fetching its configuration info, and starting in this scenario, without some independent
local caching of configuration info.

This would be bad in a three site scenario where ZooKeeper is only used for configuration.
  Normally one site up should be able to run, but in this case Zookeeper becomes an additional
fatal failure source when it rejects the read of configuration info.

Thank you,
Brian Macker


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