On 13.01.14 15:26, Vadim Bobrov wrote:
There are numerous ways (impl options) for resending messages.
Using a channel is only one.
Other than persistent channel what are the options?
In akka-persistence, channels are the only option, outside
akka-persistence, anything that can store messages re-send them if needed.
I actually believe it is important to note in the documentation that messages
in mailbox are not preserved by a processor, it was not obvious to me until I
ran a couple of tests.
From the docs:
"When a processor's receive method is called with a Persistent message
it can safely assume that this message has been successfully written to
the journal."
I think the above sentence makes that clear. If not, please make a
proposal in this thread or create a pull request.
Actually can you advise me to a design decision? Suppose I have an actor A that
receives (from outside) a lot of messages per sec. It transforms them and sends
to actor B that saves them to a database. The goal is to make sure that no
information is lost in the case of a crash and no message is sent twice. In
addition to it the journal must not grow uncontrollably. How would you
implement this? Two processors and a persistent channel in between, snapshots
and deleteMessages to control journal growth?
A single persistent channel (actor A) and a channel destination (actor
B) should be enough.
- actor A clients know from a channel's persistentReply=true that a
message has been successfully written/queued.
- actor B receives messages from A and is responsible for detecting
duplicates by tracking sequence numbers (when actor B is started it
should load the latest successfully saved sequence number from the
database).
- when actor B has successfully saved a message to the database, it can
confirm message delivery (which asynchronously removes it from the
journal - preventing unlimited journal growth).
Alternatives:
- write to the database directly (if fast enough)
- use a 3rd-party persistent messaging server
--
Martin Krasser
blog: http://krasserm.blogspot.com
code: http://github.com/krasserm
twitter: http://twitter.com/mrt1nz
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