AMQP Specification Transport

AMQP Specification.
Session
Snapshot of a Session
Endpoint
Endpoint
+- - - - - - - - - + +- - - - - - - - +
| Receiver | /| Receiver |\
/ +------------------+ \ / +----------------+ \
/ / \ \ / / \ \
/ / \ \ / / \ \
/ / \ \ / / \ \
/ / \ \ / / \ \
/ / replay buffer \ \ / / input buffer \ \
+------------+---------------------+ +------------+-------------------+
| ... C2 C3 | C4 C5 C6 C7 C8 C9 | | ... C3 C4 | C5 C6 | __ __ |
+------------+---------------------+ +------------+-------------------+
acknowledged | | | executed | received |
+-----+ | +-------------------+
| | |
+ + capacity
/ \
in-flight* blocked
C1, C2, C3: executed by the receiver, and acknowledged at the sender
C4: executed by the receiver, but not acknowledged at the sender
C5, C6: received, but not yet executed by the receiver
C7, C8: transmitted by the sender, but not yet received (in-flight)*
C9: held by the sender awaiting capacity at the receiver
* Note that should a network failure occur at this instant, the
in-flight commands will be lost. In practice, neither the
sender nor receiver knows explicitly which of the
unacknowledged commands will be lost should a network failure
occur.
4.9 Sender State
acknowledged: The id of the last command acknowledged. This marks the head of the
replay buffer.
next-command: The id that will be assigned to the next command sent on the session.
This marks the tail of the replay buffer. The id of any command in the
replay buffer must fall between acknowledged and next-command:
acknowledged < C.id < next-command for all C in the replay buffer
4.10 Receiver State
executed: The id of the last command executed. This marks the head of the input
buffer.
received: The id of the last command received. This marks the end of the filled
slots in the input buffer.
capacity: The capacity of the input buffer. The sum of executed and capacity is
the id of the command that will fill the last slot in the input buffer.
Session endpoints periodically exchange "executed", "capacity", and "acknowledged". Each endpoint uses
the knowledge of its partner's executed state to shrink the replay buffer for outgoing commands. Each
AMQP Transport v. 1-0 Page 27 of 83