Confused about the consistency guarantee of zookeeper (Sequential vs Eventual Consistency)

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EdH

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EdH Asks: Confused about the consistency guarantee of zookeeper (Sequential vs Eventual Consistency)
As I understand, Zookeeper enforces "sequential consistency" which states any execution is the same as if all read/write ops were executed in some global ordering. Basically, a client may see stale data but it's guaranteed to see values in the order of the writes which are linearized.

I have two confusions

1. How is the ordering guarantee from sequential consistency preserved when a node goes down? For example, what happens in a following scenario?

  1. Write x=1
  2. Write x=2
  3. Node A has the most recent value x=2, Node B is still on old value x=1
  4. A client reads x=2 from Node A
  5. Node A goes down.
  6. A client is now connected to Node B.
  7. A client now reads x=1 from Node B.

Doesn't this break the ordering guarantee provided by the sequential consistency?

2. Am I correct in saying that all eventual consistency model provides an ordering guarantee as long as a client is always reading from the same node?

Is the lack of ordering guarantee in eventual consistency due to the fact that a client can read from any node and is not tied to a specific node when reading a value?

(Wouldn't systems that implement sequential consistency suffer from the same issue though in a scenario where a node goes down and a client is forced to read from a client with a stale data? Kinda goes back to my question #1)

Any clarification would be greatly appreciated. Thank you.

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  • Geography
  • Replies: 0
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Files are available through the link

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