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In Cassandra, the communication between nodes is often like peer-to-peer communication, where every node talks to the other. If that’s the case, then all the nodes talk to one another, and there is a lot of communication happening. The Gossip Protocol is a method to resolve this communication chaos. In Cassandra, when one node talks to another, the node which is expected to respond, not only provides information about its status, but also provides information about the nodes that it had communicated with before. Through this process, there is a reduction in network log, more information is kept and efficiency of information gathering increases. The main feature of the protocol is to provide the latest information of any node respectively.
An important feature of Gossip Protocol is Failure Detection. Basically, when two nodes communicate with one another; for instance, Node A to Node B, then Node A sends a message ‘gossipdigestsynmessage’, which is very similar to TCP protocol to Node B. Here, Node B, once receives the message, sends an acknowledgement message ‘ack’, and then Node A responds with an acknowledgement message to Node B’s ‘ack’ message. This is known as the 3 way handshake.
If in case, the node goes down and does not send the ack message, then it will be a mark down. Even when the nodes are down, the other nodes will be periodically pinging and that is how the failure detection happens.
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