compute_ctl is mostly written in synchronous fashion, intended to run in
a single thread. However various parts had become async, and they
launched their own tokio runtimes to run the async code. For example, VM
monitor ran in its own multi-threaded runtime, and apply_spec_sql()
launched another multi-threaded runtime to run the per-database SQL
commands in parallel. In addition to that, a few places used a
current-thread runtime to run async code in the main thread, or launched
a current-thread runtime in a *different* thread to run background
tasks.
Unify the runtimes so that there is only one tokio runtime. It's created
very early at process startup, and the main thread "enters" the runtime,
so that it's always available for tokio::spawn() and runtime.block_on()
calls. All code that needs to run async code uses the same runtime.
The main thread still mostly runs in a synchronous fashion. When it
needs to run async code, it uses rt.block_on().
Spawn fewer additional threads, prefer to spawn tokio tasks instead.
Convert some code that ran synchronously in background threads into
async. I didn't go all the way, though, some background threads are
still spawned.
## Problem
In some cases, we were returning a very shallow error like `error
sending request for url (XXX)`, which made it very hard to figure out
the actual error.
## Summary of changes
Use `{:?}` in a few places, and remove it from places where we were
printing a string anyway.
## Problem
There are several parts of `compute_ctl` with a very low visibility of
errors:
1. DB migrations that run async in the background after compute start.
2. Requests made to control plane (currently only `GetSpec`).
3. Requests made to the remote extensions server.
## Summary of changes
Add new counters to quickly evaluate the amount of errors among the
fleet.
Part of neondatabase/cloud#17590
There was no value in saving them off to temporary variables.
Signed-off-by: Tristan Partin <tristan@neon.tech>
Signed-off-by: Tristan Partin <tristan@neon.tech>
