Undocumented behavior of Topic Subscription with ShoppingCart-Java

[gabizou]

The Problem

I've posted on the forums about my issue, but I have since replicated the same problem in development with the shopping-cart-java sample with a breakpoint in debugging mode, and effectively I can summarize my problem is that Topics are not producing messages in any expected and seemingly not-configurable fashion after startup. For about the first 10 minutes of the application running, messages just simply don't get published and consumed, but the aggregate states are still being updated, and events are being serialized to the Cassandra-backed event journal.

Some Backstory

Being a reactive nature, I'd personally love to be able to use Topics to be able to have reactive services with a lose coupling between services (such as the shopping cart and inventory), but I've not gotten to a point where I can verify that these behaviors of an extreme undocumented lag incurred during the first several minutes are just a byproduct of running in a development environment (using mvn lagom:runAll), or whether there are some configuration options that need to be documented in other ways?

[ignasi35]

Hi @gabizou, this is the first time we hear of such an issue. Would you be able to provide a reproducer?

[gabizou]

Would you be able to provide a reproducer?

I simply cloned the lagom/shopping-cart-java sample:

• Importing the maven pom.xml to IntelliJ
• Running the necessary docker-compose file for the services (Kafka, zookeeper, Postgres)
• Running mvn lagom:runAll with the debugger and a breakpoint at the flow subscription as line linked
• Curl curl http://localhost:9000/inventory/456 and notice the result is still 0
• Curl curl -H "Content-Type: application/json" -d 4 -X POST http://localhost:9000/inventory/456 to add 4 inventory
• Run curl -H "Content-Type: application/json" -d '{"itemId": "456", "quantity": 2}' -X POST http://localhost:9000/shoppingcart/123 to add 2 of 456 to cart
• Verify curl http://localhost:9000/inventory/456 and the inventory is still 4.......
• Wait several minutes for the debugger to actually receive the first event from the shopping cart message to update the inventory side (varies, but occasionally can be 4 minutes, sometimes up to 10 minutes, and then after this initial delay, most updates are relatively within a second).

[ignasi35]

I don't remember the details, but I think you need to checkout the shopping cart before the inventory is updated.

curl -X POST http://localhost:9000/shoppingcart/123/checkout

[gabizou]

So I did a re-test with the curl to checkout, turns out it works. My underlying problem turns out to be that https://github.com/akka/akka-persistence-cassandra/issues/867 is giving my development environment the slow-start up that I'm observing.