Wrong order of events (TrackingProcessor)

Imported from Google Groups
1

Hello together,

in one of our current projects, we have the folloging setup:

spring boot maven @ 1.5.6
axonframework maven @ 3.0.6
mongodb as event storage and mongo db as read model store

JacksonSerializer configured with the following object mapper settings:

spring.jackson.serialization.write-dates-as-timestamps=false
spring.jackson.deserialization.fail-on-unknown-properties=false
spring.jackson.deserialization.accept-single-value-as-array=true
spring.jackson.default-property-inclusion=non_null

Problem:
Some events are stored around the same second, one with 0 milliseconds and
the second some milliseconds later:

e.g. from the mongodb
{ "id:" "event1", "aggregateIdentifier": "42", "sequenceNumber": 0 "timestamp": "2017-07-17T09:08:50Z" ... }

and

{ "id:" "event1", "aggregateIdentifier": "42", "sequenceNumber": 1 "timestamp": "2017-07-17T09:08:50.139Z" ... }

Result:
In our event handlers in the read model using a tracking processor, the event are delivered in the
wrong order, the event 1 BEFORE the event 0.

Expected Result:
Event 0 before event 1

We don’t know exactly how the axon tracking processor determines the order of the events to replay,
but it seems that it has some problems with serialized timestamp. Is this maybe a wrong configuration
while serializing the date stamp or while deserializing.

Any help appreciated

Thanks in advance

Benjamin

2

Hi Benjamin,

the MongoEventStorageEngine does a sort based on the timestamp. Since this field is a String, it will use a text-based sort. The Z is higher than 1 (of the milliseconds), causing the second event overtake the first.
If possible, the serialized timestamp should always contain the milliseconds explicitly.

Axon does the serialization, in this case, and passes a String to Mongo. So far, I’ve always seen the millis being appended (even if they were 000). Will look into it.

Allard

3

Hi Allard,

thank you for your quick response, if you need more information or if I can help
you with something, let me know.

Best Regards,

Benjamin

4

Hi Benjamin,

I’ve found the issue. It’s the default formatting of Java on Instants. And because they (rightfully) add the Z for the timezone (=UTC), text based ordering of the timestamp is off when some contain millis, and some don’t.
A fix for this issue would be to explicitly provide the format to parse the instant in, and always include 3 positions for the millis.

Cheers,

Allard