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fix(db): Make idle broker polls reader-only and notify-driven (eliminates poll heartbeat UPDATEs on idle) - #362
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📝 WalkthroughWalkthroughThe state sampler now publishes queue depth on its regular cadence, eligible notification wakeups, and shutdown. Transition outcomes no longer carry ready-queue depth. PostgreSQL session polling checks read-only cases before opening a writer transaction. ChangesSampler-owned queue-depth publication
PostgreSQL session polling
Settled-request retirement
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant PollClient
participant PgBackend
participant ReaderConnection
participant PostgreSQL
participant WriterTransaction
PollClient->>PgBackend: poll_session
PgBackend->>ReaderConnection: probe_poll session state
ReaderConnection->>PostgreSQL: read session and queue state
PostgreSQL-->>ReaderConnection: probe results
ReaderConnection-->>PgBackend: direct result or writer-required result
PgBackend->>WriterTransaction: continue polls requiring writes or a claim
WriterTransaction->>PostgreSQL: recheck state and process poll
PostgreSQL-->>PollClient: poll result
Merge Risk: 🟡 Moderate · up to Ready jobs can wait up to a full long-poll window before a runner picks them up, because the new queue-depth sampler can absorb the wake meant for the runner. Cancellation or new-work signals to the root broker poll can also be missed for up to about 50 seconds. Fix the notification handling before merging. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
📝 Generate docstrings
🧪 Generate unit tests (beta)
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Bnjoroge1
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@cubic-dev-ai wdyt |
@Bnjoroge1 Direction's right, and the tradeoffs are honestly stated in the commits — this is the kind of change that's easy to argue with until you see the 3k-count(*) load-test number. The probe-then-writer split in Four things I'd double-check before merging:
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Actionable comments posted: 3
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Inline comments:
Review comments at @crates/preloop-runner-server/src/bootstrap.rs:
- Around line 1289-1290: Update the sampler loop around the `early` check so a
notification received before the one-second debounce floor expires remains
pending instead of being discarded. When the floor expires, sample the queue
depth without requiring another notification; preserve the existing five-second
interval behavior.
- Line 1276: Give the sampler a separate coalesced notification channel instead
of waiting on `shared.state.message_notify`; keep `message_notify` dedicated to
runner delivery so the sampler cannot consume a runner’s wake-up notification.
Review comments at @crates/preloop-runner-server/src/broker.rs:
- Around line 751-756: Update the root polling loop around
`message_notify.notified()` to prevent a missed `notify_waiters()` from delaying
rechecks until the full deadline. Register the notification future before
polling, or retain a bounded periodic retry such as the previous three-second
cap.
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📒 Files selected for processing (17)
crates/preloop-runner-server/src/bootstrap.rscrates/preloop-runner-server/src/broker.rscrates/preloop-runner-server/src/control/backend.rscrates/preloop-runner-server/src/control/lite/dispatch.rscrates/preloop-runner-server/src/control/lite/fork_gate.rscrates/preloop-runner-server/src/control/lite/lifecycle.rscrates/preloop-runner-server/src/control/lite/poll.rscrates/preloop-runner-server/src/control/lite/submit.rscrates/preloop-runner-server/src/control/pg/dispatch.rscrates/preloop-runner-server/src/control/pg/lifecycle.rscrates/preloop-runner-server/src/control/pg/tests.rscrates/preloop-runner-server/src/control/tests.rscrates/preloop-runner-server/src/control/types.rscrates/preloop-runner-server/src/distributed_task.rscrates/preloop-runner-server/src/runs.rscrates/preloop-runner-server/src/runtime_scheduling.rscrates/preloop-runner-server/src/state.rs
💤 Files with no reviewable changes (6)
- crates/preloop-runner-server/src/control/lite/lifecycle.rs
- crates/preloop-runner-server/src/control/backend.rs
- crates/preloop-runner-server/src/control/lite/fork_gate.rs
- crates/preloop-runner-server/src/control/lite/poll.rs
- crates/preloop-runner-server/src/control/lite/submit.rs
- crates/preloop-runner-server/src/control/pg/lifecycle.rs
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Review fixes pushed: 8d04987
CI status: |
Idle long-polling runners were the dominant writer-pool load: every poll opened a writer transaction, re-stamped last_seen_at, and re-ran the full claim scan, and the root broker handler re-polled every 3 seconds while holding the 50s request open. - poll_session now probes on the reader pool first (session, oldest message, active request, pending cancellation, ready check) and only opens the writer transaction when there is a cancellation to deliver or a claim to attempt. Ownership is still revalidated inside the writer transaction, and a probe hit that loses a race just comes back Empty, as before. - next_message_broker_ref_root waits on message_notify until the window deadline instead of re-polling every 3s, matching next_message_broker_ref and the azdo path. Heartbeats stay once per 50s window via the handlers' up-front touch_session. - retire_node_requests no longer selects already-settled requests when retiring (settle is first-result-wins, so the second settle was pure waste: ~5 statements matching zero rows per completion). - Regression tests: an idle poll leaves last_seen_at untouched, and a poll right after submit still claims.
…per operation Every submit, claim, completion, cancel and promotion ran SELECT count(*) over the jobs table to refresh a gauge whose only reader is the runner pool supervisor. At target throughput that is ~140 full scans a second for a number nobody needs exact. - The 5s state sampler already computes the ready depth (status_inputs' grouped bucket count, published as jobs.ready). It now also stores it into the node-local queue_depth atomic the co-hosted pool scales off, and mirrors it into pool_status. - Removed queue_depth from SubmitOutcome, ClaimedJob, CompleteOutcome, CancelOutcome, PromoteOutcome, EnvironmentApprovalOutcome and the azdo claim variant, plus JobSettled.queue_len (write-only). - settle_job and the cancel paths use cheap EXISTS checks for the queue_nonempty wake signal instead of the count. - Deleted the now-dead pg queue_depth()/queue_depth_on() and the uncalled pg queue_gauges helper; lite's queue_gauges no longer counts. - The per-operation ready-front labels read stays: it is one indexed LIMIT 1 row, not a full scan.
The 5s sampler now feeds the pool's queue-depth gauge, but a burst could sit up to 5s before the pool noticed - 10x the 500ms snapshot-fork provision time. The sampler loop now also wakes on message_notify (which the submit path already shouts into): Notify coalesces a flurry into one wakeup, and a 1s floor caps a sustained storm at one extra grouped count per second. Same epoll-style rhythm-plus-urgency pattern as the broker long-poll.
Review follow-ups on the poll-write refactor: - Give the state sampler its own Notify (sampler_notify). wake_waiters fires per-job notify_one permits on message_notify; a sampler parked on the same channel could steal them and strand a runner until its window ended. Every producer now wakes both channels; the LISTEN relay too. - Register the long-poll Notified before probing (enable()), in all three loops: broker ref, broker root, disttask. A notify_waiters landing between probe and registration stored no permit and was lost. - Sampler debounce naps off the 1s floor instead of dropping the event, and MissedTickBehavior::Delay prevents a burst publish after a nap. - Clamp waitSeconds to PRELOOP_MAX_POLL_WINDOW_SECS (default 60s) and floor PRELOOP_RUNNER_LIVENESS_TIMEOUT_SECS at 3x that window, so a client-chosen window can never park a runner past its own reaping. - pg probe_poll: document that claim-enabling reads must never route to a replica (they can't see writer commits). - queue_depth tests: drive a real sampler tick via test_sample_state_once (extracted from run_state_sampler) instead of asserting the removed per-operation write.
8d04987 to
bb5e992
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…ates poll heartbeat UPDATEs on idle) (#362) * Make idle broker polls reader-only and notify-driven Idle long-polling runners were the dominant writer-pool load: every poll opened a writer transaction, re-stamped last_seen_at, and re-ran the full claim scan, and the root broker handler re-polled every 3 seconds while holding the 50s request open. - poll_session now probes on the reader pool first (session, oldest message, active request, pending cancellation, ready check) and only opens the writer transaction when there is a cancellation to deliver or a claim to attempt. Ownership is still revalidated inside the writer transaction, and a probe hit that loses a race just comes back Empty, as before. - next_message_broker_ref_root waits on message_notify until the window deadline instead of re-polling every 3s, matching next_message_broker_ref and the azdo path. Heartbeats stay once per 50s window via the handlers' up-front touch_session. - retire_node_requests no longer selects already-settled requests when retiring (settle is first-result-wins, so the second settle was pure waste: ~5 statements matching zero rows per completion). - Regression tests: an idle poll leaves last_seen_at untouched, and a poll right after submit still claims. * Sample the ready-queue depth from the 5s sampler instead of counting per operation Every submit, claim, completion, cancel and promotion ran SELECT count(*) over the jobs table to refresh a gauge whose only reader is the runner pool supervisor. At target throughput that is ~140 full scans a second for a number nobody needs exact. - The 5s state sampler already computes the ready depth (status_inputs' grouped bucket count, published as jobs.ready). It now also stores it into the node-local queue_depth atomic the co-hosted pool scales off, and mirrors it into pool_status. - Removed queue_depth from SubmitOutcome, ClaimedJob, CompleteOutcome, CancelOutcome, PromoteOutcome, EnvironmentApprovalOutcome and the azdo claim variant, plus JobSettled.queue_len (write-only). - settle_job and the cancel paths use cheap EXISTS checks for the queue_nonempty wake signal instead of the count. - Deleted the now-dead pg queue_depth()/queue_depth_on() and the uncalled pg queue_gauges helper; lite's queue_gauges no longer counts. - The per-operation ready-front labels read stays: it is one indexed LIMIT 1 row, not a full scan. * Wake the state sampler early on submit bursts (debounced) The 5s sampler now feeds the pool's queue-depth gauge, but a burst could sit up to 5s before the pool noticed - 10x the 500ms snapshot-fork provision time. The sampler loop now also wakes on message_notify (which the submit path already shouts into): Notify coalesces a flurry into one wakeup, and a 1s floor caps a sustained storm at one extra grouped count per second. Same epoll-style rhythm-plus-urgency pattern as the broker long-poll. * fix: isolate the sampler's wake channel; close long-poll lost-wake race Review follow-ups on the poll-write refactor: - Give the state sampler its own Notify (sampler_notify). wake_waiters fires per-job notify_one permits on message_notify; a sampler parked on the same channel could steal them and strand a runner until its window ended. Every producer now wakes both channels; the LISTEN relay too. - Register the long-poll Notified before probing (enable()), in all three loops: broker ref, broker root, disttask. A notify_waiters landing between probe and registration stored no permit and was lost. - Sampler debounce naps off the 1s floor instead of dropping the event, and MissedTickBehavior::Delay prevents a burst publish after a nap. - Clamp waitSeconds to PRELOOP_MAX_POLL_WINDOW_SECS (default 60s) and floor PRELOOP_RUNNER_LIVENESS_TIMEOUT_SECS at 3x that window, so a client-chosen window can never park a runner past its own reaping. - pg probe_poll: document that claim-enabling reads must never route to a replica (they can't see writer commits). - queue_depth tests: drive a real sampler tick via test_sample_state_once (extracted from run_state_sampler) instead of asserting the removed per-operation write. --------- Co-authored-by: Bill Njoroge <Bnjoroge1@users.noreply.github.com>
1 participant
Phase 0 scaling fixes from the 5M-jobs design doc.
Three commits:
Load-test (2 nodes, 25 rps, 400 runners, real Postgres 16): per-op count(*) 3,063 calls/4.1s → 0. Integrity clean (0 duplicate in-flight, 0 owner mismatch, 0 SQL errors).
Based on PR #347 tip. No PR-vs-fold decision yet — opening as separate PR for review.
Summary by cubic
Eliminates the per-operation database load that dominated the writer pool at scale: idle broker polls become reader-only and notify-driven, ready-queue depth is sampled by the 5s state sampler instead of counted on every submit, claim, completion and cancel, and the sampler wakes early on submit bursts (debounced to 1/s).
notify_onepermits meant for parked runner waiters.last_seen_at; they probe on the reader pool and fall back to the writer only when a cancellation or claim is needed. Liveness re-stamping now only happens at the start of a poll window.count(*)over the jobs table (roughly 3k calls during a 4.1s load test); the sampler publishes the ready depth into thequeue_depthatomic andpool_status, and the cancel/settle paths use anEXISTScheck for the non-empty signal.message_notify, so a submit burst moves the pool gauge in milliseconds instead of at the next 5s tick; a 1s floor prevents a sustained storm from causing more than one extra count per second.waitSecondsis clamped toPRELOOP_MAX_POLL_WINDOW_SECS(default 60s) and the liveness timeout is floored at 3x that window, so a client-chosen poll can never park a healthy runner past its own reaping.last_seen_atunchanged, a poll after a submit still claims, and a parked sampler never steals a runner permit.Written for commit bb5e992. Summary will update on new commits.
Summary by CodeRabbit