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neon/control_plane/src
Christian Schwarz 035a49a6b2 neon_local start: parallel startup to break cyclic dependency (#8950)
(Found this useful during investigation
https://github.com/neondatabase/cloud/issues/16886.)

Problem
-------

Before this PR, `neon_local` sequentially does the following:
1. launch storcon process
2. wait for storcon to signal readiness
[here](75310fe441/control_plane/src/storage_controller.rs (L804-L808))
3. start pageserver
4. wait for pageserver to become ready
[here](c43e664ff5/control_plane/src/pageserver.rs (L343-L346))
5. etc

The problem is that storcon's readiness waits for the
[`startup_reconcile`](cbcd4058ed/storage_controller/src/service.rs (L520-L523))
to complete.

But pageservers aren't started at this point.

So, worst case we wait for `STARTUP_RECONCILE_TIMEOUT/2`, i.e., 15s.

This is more than the 10s default timeout allowed by neon_local.

So, the result is that `neon_local start` fails to start storcon and
stops everything.

Solution
--------

In this PR I choose the the radical solution to start everything in
parallel.

It junks up the output because we do stuff like `print!(".")` to
indicate progress.
We should just abandon that.
And switch to `utils::logging` + `tracing` with separate spans for each
component.
I can do that in this PR or we leave it as a follow-up.

Alternatives Considered
-----------------------

The Pageserver's `/v1/status` or in fact any endpoint of the mgmt API
will not `accept()` on the mgmt API socket until after the `re-attach`
call to storcon returned success.

So, it's insufficient to change the startup order to start Pageservers
first.

We cannot easily change Pageserver startup order because
`init_tenant_mgr` must complete before we start serving the mgmt API.
Otherwise tenant detach calls et al can race with `init_tenant_mgr`.

We'd have to add a "loading" state to tenant mgr and make all API
endpoints except `/v1/status` wait for _that_ to complete.


Related
-------

- https://github.com/neondatabase/neon/pull/6475
2024-09-18 18:17:55 +02:00
..
2024-07-18 09:33:46 +01:00