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40c845e57d
Instead of spawning helper threads, we now use Tokio tasks. There are multiple Tokio runtimes, for different kinds of tasks. One for serving libpq client connections, another for background operations like GC and compaction, and so on. That's not strictly required, we could use just one runtime, but with this you can still get an overview of what's happening with "top -H". There's one subtle behavior in how TenantState is updated. Before this patch, if you deleted all timelines from a tenant, its GC and compaction loops were stopped, and the tenant went back to Idle state. We no longer do that. The empty tenant stays Active. The changes to test_tenant_tasks.py are related to that. There's still plenty of synchronous code and blocking. For example, we still use blocking std::io functions for all file I/O, and the communication with WAL redo processes is still uses low-level unix poll(). We might want to rewrite those later, but this will do for now. The model is that local file I/O is considered to be fast enough that blocking - and preventing other tasks running in the same thread - is acceptable.