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 Each arrow represents either an RPC, or a write to a Kafka topic. These operations occur in the sequence indicated by the numbers next to each arrow. The sections below are numbered to match the operations in the diagram above, and describe the operation in question.

1. Finding a transaction coordinator -- the GroupCoordinatorRequest

 Since the transaction coordinator is at the center assigning PIDs and managing transactions,the first thing a producer has to do is issue a GroupCoordinatorRequest to any broker to discover the location of its coordinator.

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2. Getting a producer Id -- the InitPIDRequest

After discovering the location of its coordinator, the next step is to retrieve the producer’s PID. This is achieved by issuing a InitPIDRequest to the transaction coordinator

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