I don’t get it. How is this advantageous as it’s limited to one machine? Why wouldn’t you just have one jvm running multiple threads? What is the point of having multiple jvm processes interacting through this ring? Can someone enlighten me?
- Resource allocation; you might want to give just specific amount of memory, CPU, network I/O to specific modules of a system, which is not really feasible within a single JVM
- Resource isolation; e.g. a memory leak in one module of the system will affect just that specific JVM instance but not others (similar to why browsers run tabs in multiple processes);
- Upgrades; you can put a new version of one module of the system into place without impacting the others; while the JVM does support this via dynamic classloading (as e.g. used in OSGi or Layrry, https://github.com/moditect/layrry), this becomes complex quickly, you can create classloader leaks, etc.
- Security; You might have (3rd-party) modules you want to keep isolated from the memory, data, config, etc. of other modules; in particular with the removal of the security manager, OS-enforced process isolation is the way to
Those stops can be enough to ruin your low latency requirements in the high percentiles. A common strategy is to divide workloads between jvms so that you meet the requirement.