What are the knowledge points of Storm ACK framework
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1: in the design of the Ack framework, messages emitted by Storm correspond to a random message ID number.
2: after Spout launches the message. A message will be sent like Acker Bolt, and the content of the message is "RootID, message ID" Acker Bolt will create for the message
Create a tracking item
3: during the process of generating the message to be transmitted by Bolt, the message ID will also be sent to AckerBolt, and AckerBolt will XOR the message ID and store it later.
4: in the process of Ack the input message, Bolt will also send the message ID to AckerBolt,Acker Bolt for the message ID or store it later, because the message has already sent ID to AckerBolt when it is sent, and then the message ID will be sent again when it is Ack, which is equivalent to the end of the tracking of the message.
When 5:Acker Bolt updates the tracking value of a message, if it is found that its value changes to 0, it will be like the message sent by the Spout node, table name, and the message sent by Spout has been successfully processed.
6: the message ID of all messages will be updated to the root (/ root) tree. The root message is the message sent by Spout, and the new message generated by Bolt will not be tracked separately.
7: if you do not specify an ID for message tracking during the launch process, the system will not track the message, and if the system does not contain Ack bolt, the message will not be tracked.
8: the tracking capacity load of each message of Spout and the message evolved from this message is: "16 bytes", 8 bytes of root message ID, and 8 bytes of message tracking value "AckValue". In fact, because HashMap is used to trace it in Storm, in 32-bit JVM, each message needs at least 20 bytes of additional load, so the tracking of a message requires about 40 loads.
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