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Elaborating on the message send semantics as per the ticket

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Viktor Klang 2011-12-08 12:09:19 +01:00
parent 4803ba517c
commit d7771dc596
2 changed files with 35 additions and 8 deletions
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2
akka-docs/general/index.rst
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@ -5,9 +5,9 @@ General
:maxdepth: 2 :maxdepth: 2
jmm jmm
message-send-semantics
configuration configuration
event-handler event-handler
slf4j slf4j
addressing addressing
supervision supervision
guaranteed-delivery

41
akka-docs/general/guaranteed-delivery.rst → akka-docs/general/message-send-semantics.rst
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@ -1,13 +1,14 @@
.. _guaranteed-delivery: .. _message-send-semantics:
##################### #######################
Guaranteed Delivery Message send semantics
##################### #######################
Guaranteed Delivery
=================== Guaranteed Delivery?
====================
Akka does *not* support guaranteed delivery. Akka does *not* support guaranteed delivery.
@ -39,4 +40,30 @@ application and can solve it fastest and most reliable by explicit ``ACK`` and
``RETRY`` (if you really need it, most often you don't). Using Akka's Durable ``RETRY`` (if you really need it, most often you don't). Using Akka's Durable
Mailboxes could help with this. Mailboxes could help with this.
.. _Erlang documentation: http://www.erlang.org/faq/academic.html Delivery semantics
==================
At-most-once
------------
Actual transports may provide stronger semantics,
but at-most-once is the semantics you should expect.
The alternatives would be once-and-only-once, which is extremely costly,
or atleast-once which essentially requires idempotency of message processing,
which is a user-level concern.
Ordering is preserved on a per-sender basis
-------------------------------------------
Actor ``A1` sends messages ``M1``, ``M2``, ``M3`` to ``A2``
Actor ``A3`` sends messages ``M4``, ``M5``, ``M6`` to ``A2``
This means that:
1) If ``M1`` is delivered it must be delivered before ``M2`` and ``M3``
2) If ``M2`` is delivered it must be delivered before ``M3``
3) If ``M4`` is delivered it must be delivered before ``M5`` and ``M6``
4) If ``M5`` is delivered it must be delivered before ``M6``
5) ``A2`` can see messages from ``A1`` interleaved with messages from ``A3``
6) Since there is no guaranteed delivery, none, some or all of the messages may arrive to ``A2``
.. _Erlang documentation: http://www.erlang.org/faq/academic.html