infinispan-spring-boot | Infinispan Spring Boot starter | Model View Controller library

My app uses Infinispan's Spring Session implementation via the Infinispan Spring Boot Starter. I am using the embedded mode via InfinispanEmbeddedHttpSessionConfiguration. The Spring Session integration documentation is pretty sparse, and it doesn't mention anything about the recommended cache mode for the session cache.

I have been using the DIST_SYNC mode, but I notice occasional ConcurrentModificationException errors in the log. Is there a more appropriate cache mode, or could this be a bug?

I am using Spring Boot 2.2.10, Infinispan 9.4.20 and Spring Session 2.2.0. The app runs under JDK 11.

Edit

The exception I observe in the logs is below. I've put xxx. in place of my company's package names for our filters.

The exception occurs when the same session is reused in quick succession, in particular when our external security vendor runs weekly scans on our app. The exception does not occur every week. When it does occur, it leads to an eventual OutOfMemory error on the node that did not get the ConcurrentModificationException. The heap is full of TrianglePerCacheInboundInvocationHander$1 objects.

I have tried to reproduce the error in our development environment by running concurrent requests for 3 days, but to no avail.

I've looked at the Infinispan Spring Session code, and I see that each request gets its own instance of MapSession, materialised from the serialised data stored in Infinispan. I don't see how multiple concurrent requests for the same session could cause the ConcurrentModificationException, and I'm not aware of anywhere in my app that would allow concurrent access to a MapSession instance from multiple threads.