Database Reference
In-Depth Information
Figure 21-2. Reads are satisfied by followers, whereas writes are committed by the leader
Every update made to the znode tree is given a globally unique identifier, called a zxid
(which stands for “ZooKeeper transaction ID”). Updates are ordered, so if zxid z 1 is less
than z 2 , then z 1 happened before z 2 , according to ZooKeeper (which is the single authority
on ordering in the distributed system).
The following guarantees for data consistency flow from ZooKeeper's design:
Sequential consistency
Updates from any particular client are applied in the order that they are sent. This
means that if a client updates the znode z to the value a, and in a later operation, it up-
dates z to the value b, then no client will ever see z with value a after it has seen it with
value b (if no other updates are made to z).
Atomicity
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