[GitHub] [zookeeper] chingchan1996 commented on a change in pull request #1444: ZOOKEEPER-3922: The introduction of the oracle, a failure detector.

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chingchan1996 commented on a change in pull request #1444:
URL: https://github.com/apache/zookeeper/pull/1444#discussion_r508170716



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File path: zookeeper-docs/src/main/resources/markdown/zookeeperOracleQuorums.md
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+
+# Introduction to Oracle Quorum
+
+The introduction to Oracle Quorum increases the availability of a cluster of 2 ZooKeeper instances with a failure detector
+ as known as the Oracle. The Oracle is designed to grant the permission to the instance which is the only remaining instance
+in a 2-node configuration when the other instance is identified as faulty by the fail detector, the Oracle.
+
+## The implementation of the Oracle

Review comment:
       In the previous deployed context, the oracle is a text file which contains either 0 or 1. 0 means the other instance is not faulty, and vice versa. Due to the heterogeneous deployed contexts, the ways of implementation of an Oracle are not defined. An example could be a hardware device which could distinguishes whether the machine is power on or not. Based the information, the device could update the file on the instance to 0 or 1. Another example could be another process within the same machine as the zookeeper instance constantly check the other instance is alive or not, for instance, by pinging the other node , and bases the information to update the oracle file. In the case for hard to find two dedicated hardware, we could use docker to stimulate a two-node systems (https://github.com/chingchan1996/Docker_ZooKeeper), and manually cause failures and update the oracle files. 




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