Limit pending poll notification tasks

[dahlia]

Repeated expiry changes can fill the shared task queue with delayed poll notifications. Coalesce wakeups by poll ID and cap stored poll tasks, including retries, at 100 under a PostgreSQL transaction lock. Queue rows serve as reservations, so consuming a task cannot leave a stale marker that blocks rescheduling.

At capacity, earlier wakeups replace later ones; the existing expiry recovery scan picks up displaced or deferred polls. Delayed inserts skip NOTIFY and use Fedify's queue polling to avoid allocating a timer in every worker.

Fixes #653.

Summary by CodeRabbit

• Improvements
  • Poll notifications share a queue capped at 100 pending messages. Repeated schedules for the same poll are combined, and earlier wakeups take priority when the queue is full.
  • Delayed or displaced notifications can be recovered after expiry. Recovery pauses when the shared ready queue reaches 200 messages.
• Documentation
  • Updated worker installation guides with queue behavior, monitoring details, and SQL queries for checking queue counts.

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No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between f97fe72 and f2221a3.

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• docs/src/content/docs/ko/install/workers.mdx

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• docs/src/content/docs/ko/install/workers.mdx

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📝 Walkthrough

Walkthrough

Poll notification scheduling now uses a PostgreSQL-backed queue that coalesces tasks by poll and limits stored poll messages to 100. The change adds admission and recovery tests, and documents queue behavior, upgrade handling, and monitoring in five language versions.

Changes

Poll Notification Queue

Layer / File(s)	Summary
Poll task admission and queue integration src/background/poll-queue.ts, src/poll-notification-tasks.ts, src/federation/federation.ts	PollMessageQueue limits stored poll tasks, coalesces tasks by poll ordering key, and defers admission when capacity or the admission lock prevents insertion. Poll scheduling and the federation task queue use the new queue.
Recovery and queue workload validation src/background/poll-queue.test.ts	Integration tests cover queue bounds, coalescing, expiry changes, recovery, retries, listener delivery, large unrelated backlogs, and mixed workloads with two consumers.
Queue operations and monitoring documentation CHANGES.md, docs/src/content/docs/install/workers.mdx, docs/src/content/docs/{ja,ko,zh-cn,zh-tw}/install/workers.mdx	The changelog and worker guides describe queue limits, delayed wakeups, recovery conditions, upgrade handling, rate-limited warnings, and SQL queries for queue counts.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant PollScheduler
  participant PollMessageQueue
  participant PostgreSQL
  participant QueueListener
  PollScheduler->>PollMessageQueue: enqueue poll task with ordering key
  PollMessageQueue->>PostgreSQL: coalesce or admit task under limit
  PostgreSQL-->>PollMessageQueue: return queue result
  PollMessageQueue->>QueueListener: notify for immediately due task

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Merge Risk: ⚪ Minimal · up to f2221

The queue limit and worker guidance show no actionable issue in the reviewed change. This review identifies no reason to delay merge beyond normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to f97fe

The change limits accumulated poll work without adding new privileges or changing notification recipients. Transactional admission and durable recovery provide useful safeguards. Delivery remains conditional on available worker capacity, and the limit requires all producers to run the updated code.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The resource-control scope is the shared database's poll-task pool, not an individual account. Actors able to trigger eligible poll schedules share that budget with other local users. Non-poll tasks bypass poll admission, and the cap does not bound running handlers or recipient fanout.

Security Findings and Attack Paths

• inferred — Repeated eligible scheduling reaches shared queue storage through the existing task path. The new per-poll coalescing and serialized admission constrain this previously unrestricted accumulation. Saturation can defer another poll's wakeup, but durable recovery remains available; the inspected comparison does not establish a new privilege escalation, recipient-control bypass, or materially worsened attack path.

Trust Boundaries and Controls

• observed — Admission classification checks the task envelope's type and exact task name; it does not itself validate pollId or authorize recipients. The existing registered task supplies UUID payload validation, and notification execution derives recipients from current database ownership and votes rather than accepting recipient authority from the queued message.

Resilience and Maintainability Implications

• inferred — Recovery repairs consumed, displaced, or deferred work without detached reservations. Existing poll-row locking and owner/poll duplicate checks contain repeated delivery. Eventual delivery remains conditional: recovery pauses under shared ready-queue pressure, so sustained overload can delay notifications despite the storage bound.

Hardening Proposals

• proposed — Preserve explicit dependency-upgrade checks for the queue table layout, remove-before-handler behavior, retry routing, and delayed polling. The adapter's direct SQL makes these contracts relevant to preventing admission-control drift.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 4 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: limiting pending poll notification tasks.
Linked Issues check	✅ Passed	Issue #653 requires bounded pending poll work, safe expiry changes, recovery, duplicate-safe delivery, tests, and queue-limit documentation with monitoring guidance. The whole-PR evidence and prior as…
Out of Scope Changes check	✅ Passed	The only change since the prior review updates the Korean worker guide’s description of wakeup timing. It remains related to documenting poll notification behavior. The whole-PR changes implement, tes…

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 4 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @docs/src/content/docs/ko/install/workers.mdx:
- Line 115: In the Korean workers guide, update the sentence at the wakeup
description to say it rereads the current expiry time, replacing “현재 시각” with
“현재 만료 시각”; leave the rest of the sentence unchanged.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 04c2d3f1-183c-45ea-a2b9-2ab8bc497aa2

📥 Commits

Reviewing files that changed from the base of the PR and between e28d73f and f97fe72.

📒 Files selected for processing (10)

• CHANGES.md
• docs/src/content/docs/install/workers.mdx
• docs/src/content/docs/ja/install/workers.mdx
• docs/src/content/docs/ko/install/workers.mdx
• docs/src/content/docs/zh-cn/install/workers.mdx
• docs/src/content/docs/zh-tw/install/workers.mdx
• src/background/poll-queue.test.ts
• src/background/poll-queue.ts
• src/federation/federation.ts
• src/poll-notification-tasks.ts

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