Shulou(Shulou.com)06/03 Report--

Zookeeper is a reliable coordination system for large distributed systems.

1) it provides functions such as configuration maintenance, name service, distributed synchronization, group service, etc.

2) its goal is to encapsulate complex and error-prone key services, and to provide users with simple and easy-to-use interfaces and systems with efficient performance and stable functions.

Features:

1, final consistency: show the client the same attempt

2. Reliability: if a message is accepted by one server, it will be accepted by all servers.

3, real-time: zookeeper can not guarantee that two clients can get the newly updated data at the same time. If you need the latest data, you should call the sync () API before reading the data.

4. Wait irrelevant (wait-free): slow or invalid client does not interfere with fast client requests.

5, atomicity: the update operation either succeeds or fails, with no intermediate state.

6. Sequence: for all server, the same message is published in the same order.

Basic principles

There are many server, which can be divided into master and subordinate, but there is one leader and the other is follower.

Each server has a piece of data in memory. When it is started, a leader will be elected according to the poxos protocol.

Leader handles data update operations, using the zab protocol

A sign of a successful update operation, most of the server is in memory, and the data is modified successfully (one has 5, 3 have been written successfully)

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