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DB Quorum explanatoin

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#1
  • Dynamo replicates writes to a sloppy quorum of other nodes in the system, instead of a strict majority quorum like Paxos. All read/write operations are performed on the first NN healthy nodes from the preference list, which may not always be the first NN nodes encountered while walking the consistent hashing ring.

Can someone help with detailed explanation for this?

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#2

Hi @Ayush_Gupta, Thank you for contacting the Educative team with your query!

To understand this we should know about sloppy quorum, R/W is the minimum number of nodes that must participate in a successful read/write operation. Setting R + W > N yields a quorum-like system. In this model, the latency of a get (or put) operation is dictated by the slowest of the R (or W) replicas. In dynamo, when the available replicas are less than the total replicas sloppy quorum is used to ensure read availability. In this context, sloppy quorum in Dynamo means hints stored in nodes other than the replicas count towards reading consistency requirements; hence, improving read availability.

Hope the answer to your query.
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#3

Unless hinted handoff is not done, this doesnt improve read availability. Can you confirm if Iā€™m missing something?

Course: Educative: Interactive Courses for Software Developers
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#4

Hi @Ayush_Gupta,
Transient failures are handled with the hinted handoff. If the replica that was hinted at was no longer available? Dynamo has an anti-entropy protocol to deal with these circumstances and maintain the replicas in sync. To discover inconsistencies and reduce the amount of data sent, a Merkle Tree is utilized.
Merkle Tree : Merkle Tree

Hope the answer to the query !

#5

For some reason, im unable to attach the link : scalablehuman ā†’ distributed-data-intensive-systems-sloppy-quorums-and-hinted-handoffs.

Article says if node will take handoff from backup/neighbour node. Question : till this handoff is done, how does consistency works?

Course: Educative: Interactive Courses for Software Developers
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