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From Jordan Zimmerman <jor...@jordanzimmerman.com>
Subject Re: Consistency Guarantees
Date Sun, 18 Aug 2019 18:34:33 GMT
ZooKeeper _is_ linearizable. I’m pretty sure the ZAB paper talks about it. Aphyr does as
well here: https://aphyr.com/posts/291-jepsen-zookeeper

Jordan Zimmerman

> On Aug 18, 2019, at 1:23 PM, Karolos Antoniadis <karolos@gmail.com> wrote:
> Hello everyone,
> I was wondering on the exact consistency guarantees that ZooKeeper provides.
> It seems that ZooKeeper does not provide strong consistency (i.e.,
> linearizability) since reads could potentially return arbitrarily old
> values.
> On the other hand, ZooKeeper provides sequential consistency, since the
> order of operations of a specific client is respected and all operations
> appear to take place in some total order (
> https://jepsen.io/consistency/models/sequential).
> However, ZooKeeper provides linearizable writes, and therefore it provides
> something stronger than sequential consistency, but still not as strong as
> linearizability. In other words, ZooKeeper guarantees are somewhere between
> sequential consistency and linearizability.
> Is there a specific name for the specific consistency guarantees that
> ZooKeeper provides?
> What would the ZooKeeper community claim about the consistency guarantees
> of ZooKeeper?
> Best Regards,
> Karolos

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