I wanted to start this issue to collate all of the configurations which use very old default values, that we might consider changing. The immediate ones that come to mind:

replica-lazy-flush no -> yes
lazyfree-lazy-user-flush no ->yes

There are many problems with running flush synchronously. Even in single CPU environments, the thread managers should balance between the freeing and serving incoming requests.

We should probably also revisit all of the datastructure limits (set-max-listpack-entries for example), which were probably tuned in a world with CPUs from a decade ago.