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`temps serve` created two multi-threaded tokio runtimes: one to run the three startup `block_on`s (database connection, private-address setting, console version) and, further down, the long-lived one that drives the index build, the backfill, the listeners and the console. The first was never dropped. Shadowing does not drop the shadowed value, and the function only returns when the process ends, so its worker threads -- one per CPU -- stayed alive for the life of the process doing nothing. Build the long-lived runtime up front and use it for the startup work too, removing the second runtime entirely. The runtime has to be the multi-threaded one, and it has to be created before the pool rather than after: sqlx spawns a pool-maintenance task when the pool is constructed, and every socket the pool opens (`min_connections`, plus the connection migrations run on) registers with the creating runtime's IO driver. Creating the pool on a runtime that stops being driven strands both, and the first query from the main runtime hangs. That is also why the similar-looking startup runtime in `serve/proxy.rs` is left alone -- it spawns the on-demand TLS cert consumer, which has the same requirement.
📓 Changelog previewThis is what your commits will add to the generated ## [Unreleased]
### Documentation
- **cli:** Correct the serve runtime lifetime comment
### Performance
- **cli:** Build the serve runtime once, before the database pool |
📝 WalkthroughWalkthroughThe serve command now creates one long-lived Tokio runtime before database pool creation. The runtime remains active for database operations, background tasks, listeners, and server execution. Post-migration tasks reuse this runtime instead of creating another one. ChangesRuntime lifecycle
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: ⚪ Minimal · up to The change removes an unused runtime while preserving server behavior. The remaining issue is limited to an inaccurate explanatory comment about when the runtime is dropped; no actionable merge-blocking risk remains. Poem
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@crates/temps-cli/src/commands/serve/mod.rs`:
- Around line 192-205: Update the runtime lifetime comment near the long-lived
runtime construction to accurately state that rt is dropped when
execute_with_extra_plugins returns and that the console path does not run
Pingora; remove claims that it is never dropped or that Pingora holds the
thread, while preserving the explanation of why the pool must be created on this
runtime.
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The comment claimed the runtime is never dropped because pingora holds the thread. That is only true for `--role=all`. Under `--role=console` the function returns from `rt.block_on` on the console future and the runtime is dropped there; pingora never runs on that path.
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Description
Summary
temps servebuilt two multi-threaded tokio runtimes. The first (serve/mod.rs:193) ran the three startupblock_ons — database connection, private-address setting, console version — and was then never used again. The second, created ~120 lines later, is the long-lived one that drives the index build, the backfill, the listeners and the console.The first one was never dropped. Shadowing a binding does not drop the shadowed value: it stays alive, unreachable, until the end of scope, and drops run in reverse declaration order. Since
execute_with_extra_pluginsonly returns when serving ends, its worker threads — one per CPU, viaavailable_parallelism()— lived for essentially the whole life of the process doing nothing.This builds the long-lived runtime up front and uses it for the startup work too, deleting the second runtime entirely.
Why it is safe
The runtime has to stay multi-threaded, and it has to be created before the pool rather than after. Shrinking the startup runtime to
new_current_thread()instead — the obvious-looking alternative — silently breaks the server:sqlxspawns a pool-maintenance task when the pool is constructed (sqlx-core-0.8.6pool/inner.rs:70→spawn_maintenance_tasks→rt::spawn).establish_connectionsets.idle_timeout(600s), so it takes the long-lived looping branch, not the shortmin_connectionsone.establish_connectionsets.min_connections(5), so five sockets plus the connection migrations run on are bound to that runtime.If the creating runtime stops being driven, both are stranded — the maintenance task unpolled, the pooled sockets bound to a driver nothing runs — and the first query issued from the main runtime hangs forever. Reproduced with the real sea-orm pool, the real pool options and a real PostgreSQL, A/B/A/B:
Creating the pool on the runtime that will keep driving it sidesteps the whole class of problem, which is why this moves the runtime up rather than shrinking it.
The similar-looking startup runtime in
serve/proxy.rsis deliberately left alone. It builds the on-demand TLS cert manager, whosespawn_consumercallstokio::spawn; after that pingora blocks the thread. With a multi-threaded runtime the workers keep polling the consumer. Converting it would leave the TLS callback'stry_enqueuejobs unprocessed — a silent failure that only shows up when on-demand TLS is configured. Same hazard, different mechanism (an explicittokio::spawnrather than sqlx's internal one), and out of scope here.Nothing else in the moved runtime's scope needs to outlive its
block_on: the only uses are the three sequentialblock_ons, and all laterrt.spawncalls land on the same runtime they always did.Cost
Measured, not estimated: local PostgreSQL 16 with TimescaleDB and pgvector,
serve --role=all, sampled from/proc/<pid>/status8s after✅ Console API is ready. No swap on the box at all (Swap: 0), so RSS cannot be hidden. Runs interleaved A/B.On this 4-CPU machine (4 runs each):
With
TOKIO_WORKER_THREADS=24, to show how it scales on a bigger box (3 runs each):The thread saving is exactly one runtime's worth and is deterministic: −4 workers natively, −24 at
TOKIO_WORKER_THREADS=24(77 → 53 in every run).The memory saving is not measurable, and this PR should not be sold as one. Even with 24 threads removed the VmRSS delta is −1.4 MB against a 3.6 MB spread between runs — noise. Startup time is unchanged in both directions.
So the case for this change is hygiene, not megabytes: an entire multi-threaded runtime was being held for the life of the process to do nothing, and its cost grows linearly with CPU count with no ceiling. On the documented minimum (2 cores) it saves 2 threads; on a 24-core box, 24.
Validation
cargo check --lib— clean, no code warnings (only pre-existing build-script notices about the web build being skipped in debug).cargo fmt --check— clean.temps servebrought fully up against a real PostgreSQL + TimescaleDB and driven to✅ Console API is readyon both binaries, 7 runs each — migrations, index build, backfill, listeners, proxy bind and console all exercised on the consolidated runtime.cargo test --liblocally reported337 passed; 1 failedintemps-agents. The failure issandbox::docker::tests::test_pull_fallback_on_missing_hub_image, and it is an artifact of my local sandbox, not this change: the test falls back to building an image that installs Node over the network, and my local docker daemon was started with--iptables=false, so containers have no egress (confirmed directly —docker pullworks, egress from inside a container does not). Independently of that, the PR touches exactly one file andcrates/temps-agentsis byte-identical to the base branch, and the dependency runstemps-cli → temps-agents, not the reverse. CI runs the same test with working Docker and it passes.Note for a follow-up, not addressed here:
serve/mod.rsstill builds a third multi-threaded runtime for the Docker capability probe, andserve/proxy.rsits own. Neither is touched by this PR.Type of change
Checklist
cargo test --lib) — green in CI; the single local failure is an unrelated Docker test broken by my sandbox's container networking, see Validation.cargo check --libpasses with no warningsRelated issues
None.