In summary, within the database clusters used for the NHS Spine, historically we have used the primary write option (pw=2) to ensure data isn't lost due to individual hardware failures, as a proxy for physical diversity guarantees. This has worked well, however can lead to
a situation where a riak database cluster rejects some writes in the case of two node failures.
The solution is to more directly tie configuration options over diversity to the physical layout of the system at run-time, not the abstract concept of the ring, and the new node_confirms option allows operators to specify the number of diverse nodes that must
confirm their writes before a write is considered successful.
Next Friday Martin (@masleeds) is planning to do a write-up of the testing so far of
the core node_worker_pool to help with multi-data-centre anti-entropy.
Dr Ramen Sen
Lead Systems Engineer
Operations and Non-functional Test Lead
Spine 2 Core
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