Hi Jacek,
you can achieve that by overriding the methods onReplaySuccess and
onReplayFailure in akka.persistence.View. Only problem is that their
visibility is private[persistence] in the latest release, so you'd need
to place your implementation class in the akka.persistence package as a
workaround. There is already a ticket that discusses sending special
messages to processors (and views) after (incremental) message replays.
This would then offer a public API for your use case.
With the described workaround:
EVENT A = onReplayFailure call (several times, depending on how long the
backend store is unavailable)
EVENT B = first received message after backend store became available
again (0..n messages)
EVENT C = onReplaySuccess call
Hope that helps.
Cheers,
Martin
On 28.04.14 21:38, Jacek Dąbrowski wrote:
Hello,
I'm trying to figure out, how to handle journal failures with
akka-persistence Views.
Imagine the following scenario:
1. Processor (actor system 1) writes messages 1-10
2. Processor (actor system 1) writes messages 11-20
3. View (actor system 2) reads messages 1-10
4. Journal crashes
5. <View: detect that journal is dead> - EVENT A
6. <View: detect that journal is back up> - EVENT B
7. <View: read messages 11-20 from the journal> - EVENT C
8. <View: resume normal operation> - back to normal processing
The View is processing a slice of configuration that critically
impacts the program's main request handling function. What I'm trying
to achieve is to detect events: A, B and C, and wrap the programs
logic around them, e.g. enqueue requests between events A and C,
perform some kind of reload on event B.
Is this possible with akka-persistence? If not, maybe at least
detecting journal failure after a couple of polling attempts fail?
Best regards,
--
Jacek
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