How to sinchronize transactions with sorted lists?

[faermanj]

Hello,

I'm trying to build a simple transaction processing demo (credit / debit / balance) using infinispan (embedded) in two API nodes.
I've setup pessimistic locking and timeout, like this:
https://github.com/CaravanaCloud/rinha-de-backend-2024-q1-impl/blob/main/rinhadebackend/src/main/archived/ispn/CacheProducer.java

And trying to process transactions like this...

write transaction (credit/debit):
https://github.com/CaravanaCloud/rinha-de-backend-2024-q1-impl/blob/69753ac034402d7463b55aa5e18c77af7ca65c76/rinhadebackend/src/main/archived/ispn/CachedServlet.java#L115

read transaction (balance, 10 latest)
https://github.com/CaravanaCloud/rinha-de-backend-2024-q1-impl/blob/69753ac034402d7463b55aa5e18c77af7ca65c76/rinhadebackend/src/main/archived/ispn/CachedServlet.java#L227

However, the application fails to properly synchronize access to the data, resulting in overrides and failures to keep balance consistent.

There are no errors or exceptions on the consoles, all seems to be working as expected.

I'm quite new to infinispan and not sure how to proceed, any clues would be greatly appreciated, because i have none :)

Thanks in advance,
Julio

[pruivo]

It overrides because you are modifying the same instance. Infinispan does not do any cloning when storing or loading the instance. My advice is to make your Cliente class immutable or make sure you create a new instance before modifying it.

To be on the safer side, both keys and values should be immutable.

[faermanj]

The issue is that, if I send several transaction requests simultaneously, the balance gets corrupted.
I believe that would be because the lists are obtained, changed, and put back in overlap.
From the application, what I can see is the stress tests failing (they pass on relational databases) with errors indicating that the sum and order of transactions is different from the expected.

[faermanj]

An example for reference. No errors in server or infinispan logs.

[pruivo]

If you provide the logs, I can figure out what's going on.

[faermanj]

@pruivo cool, i appreciate the helpout, i'll record a brief demo

[faermanj]

Here's a shot of the console logs, it's stable so i believe infinispan is working as expected, but my code or configuration is missing something.

[faermanj]

Here's a brief demonstration of the issue:
https://www.loom.com/share/faf63e1e1464409abd2b07d27105551c?sid=5a3ead4f-0551-474e-9084-2b0210dce71c

And here's the code:
https://github.com/CaravanaCloud/rinha-de-backend-2024-q1-impl/blob/main/rinhadebackend-ispn/src/main/java/caravanacloud/ispn/CachedServlet.java

Thanks!

[pruivo]

May I ask about https://github.com/CaravanaCloud/rinha-de-backend-2024-q1-impl/blob/a18a20da050d909ad12e8702cdf7b67a4c7209ca/rinhadebackend-ispn/src/main/java/caravanacloud/ispn/Cliente.java#L93-L95 ?
You're blindly dropping transactions and couldn't that explain why the balance doesn't add up in your stress test?

[faermanj]

Sure! The balance request (extrato) is expected to return the current balance and the 10 latest transactions, that's why the list is cut to this size and created with the comparator by date.

[pruivo]

Is there an easier way for me to try and debug it?
I have a couple of concerts:

• The PriorityQueue is sorted from the most recent to the older transaction but, the poll() method will remove the most recent transaction.
• The project says, the JSON response must have the latest 10 transactions, but you need all of them to compute the correct balance.

ps. the challenge looks interesting 👍

[faermanj]

Sure thing, I'll post a new recording of how to run the working and non-working versions, it's all super simple and ready to run on gitpod.
The balance aspect is correct, similar to a real bank, I can see my all-time balance and latest transactions, expected not to match, that's fine. What I'm suspecting is that, somehow, the list is being changed simultaneously on both servers.
Thanks a lot for the helpout!

[faermanj]

Here's how to run the project, how I expected transactions to work and how it's failing.
Thanks in advance for the helpout!
https://www.loom.com/share/6a78f8904caf429d850af786fcd84463

[faermanj]

Here's a link to the repo:
https://github.com/CaravanaCloud/rinha-de-backend-2024-q1-impl

And to start it on a gitpod:
https://gitpod.io/#github.com/CaravanaCloud/rinha-de-backend-2024-q1-impl