Tweak

Chapter 7.1 --- Jepsen.ipynb

@@ -140,7 +140,17 @@
  "* It is not.\n",
  "* It is basically a CP database that blocks forever when a partition occurs. \"Trivial availability\" according to one reading of the conjecture.\n",
  "\n",
- "## Kafka"
+ "\n",
+ "## Kafka\n",
+ "\n",
+ "* Kafka is a message broker, not a database. It added replication as a feature.\n",
+ "* Kafka replication is based on a two-tier architecture.\n",
+ "* Brokers that ack right up to the latest write compose an in-sync replica set. The system will continue to operate normally in the case of broker failures, right up to only having a single broker alive.\n",
+ "* Brokers push to data replicas, which handle actually storing the data. The data replicas are handled by Zookeeper, and are majority quorom based. Thus they can tolerate only N/2 failures.\n",
+ "* Brokers are more resiliant than the underlying data store.\n",
+ "\n",
+ "\n",
+ "* Jepsen showed that a complex failure in both the broker and the node layer can cause lost updates."
  ]
  }
  ],