[sumedh-aerram]

Summary

Fixes #2288.

The PostgreSQL watcher saved its read head as the resume token. It moved the cursor when an event was enqueued on the 100-slot channel, and MarkProcessed persisted that cursor. So acknowledging event 1 while events 2–5 were still buffered or in flight saved a position after event 5, and a restart skipped 2–5.

The watcher now saves the newest position with no unacknowledged delivery before it:

• Delivery tracking. Each delivery's (changed_at, id) and a delivery sequence number are recorded under the watcher lock before the event is sent on the channel. That takes one lock acquisition per delivery, the same as before.
• Saved token. The token saved is the minimum of the read cursor and the strict predecessor (changed_at, id-1) of every pending delivery. With nothing pending, it is the cursor, as before. It can move backward, which means replay, never skipping. It also holds behind late NOTIFY rows below the cursor and the out-of-order rows from fix(store-client): advance the PostgreSQL change stream cursor in poll order #2265.
• Ack contract, now documented on both ChangeStreamWatcher interfaces. MarkProcessed(X) acknowledges the earliest pending delivery with id X and every delivery handed out before it (cumulative in delivery order). This matches MongoDB resume tokens, the partitioned processor's LowWaterMarkTracker and event-exporter's sequenceTracker. Empty and unknown tokens certify nothing.
• Acks no longer move the read cursor. Before, a token ahead of the cursor could skip unread rows. highestReadEventID still lets timestampForAck (fix(store-client): never advance the PostgreSQL resume position past an unverified event #2250) skip the lookup for rows already read.
• Abandoned sends stay pending. If a send is abandoned on Close or context cancel, the delivery stays pending. A shutdown flush, such as the partitioned processor's final watermark, can't save past a row that was never handed out.
• Bounded memory, never blocks. At 4,096 pending deliveries, the oldest entry is evicted into a floor that the saved token can't pass. Any ack of a still-tracked delivery covers everything evicted (cumulative contract) and clears the floor. Delivery never blocks. A blocking cap could deadlock node-drainer, which doesn't ack failed preprocessing, during a long outage.

The UPDATE ... processed = TRUE WHERE id <= $1 is unchanged. Nothing in production reads processed for delivery.

Behavior change: checkpoint write failures now return an error

saveResumePosition errors used to be logged and dropped, so MarkProcessed returned nil after failing to persist. They now propagate, as ADR-068's protocol requires. Per caller:

Caller	Consequence
Analyzer, default serial processor	Processor stops, analyzer exits, pod restarts and replays
Analyzer, partitioned processor	Logs and keeps its watermark for retry; doesn't stop
event-exporter	Worker pool cancels; exporter exits and restarts
fault-quarantine	Stream returns an error; component exits and restarts
fault-remediation	Terminal-path errors requeue and re-run the reconcile; malformed-event paths log and continue
node-drainer	Logs and continues

Happy to split this out if you'd rather review it separately.

Caller audit and follow-ups

Every production MarkProcessed caller was checked against the cumulative contract. Serial processors, the partitioned processor, event-exporter and fault-quarantine all ack in delivery order or as a contiguous watermark. Two callers don't:

• fault-remediation can ack a later event while an earlier one is requeued for an in-progress CR.
• node-drainer acks past events whose preprocessing failed.

As the maintainers pointed out on #2348 and #2349, neither loses events on restart. Both components re-derive pending work from database state at cold start (HandleColdStart, coldstart.Handle), so the resume token isn't what recovers those events. This PR doesn't change either caller.

Known limits:

• If the same id is redelivered while the earlier copy has been evicted, an ack can over-certify. That needs saturation and a redelivered id together.
• Eviction copies the 4,096-entry slice per delivery while saturated.
• ADR-054 lag still measures read progress.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📚 Documentation
• 🔧 Refactoring
• 🔨 Build/CI

Component(s) Affected

• Health Monitor
• Core Service
• Fault Management
• Janitor
• Deployment/Config
• API/Interface
• Preflight
• Plugins
• Documentation/CI
• New Component
• Multiple Components
• Other

Testing

• Tests pass locally
• Manual testing completed
• No breaking changes (or documented)

Unit tests (sqlmock, deterministic, using testing/synctest):

• Buffered restart replay and cumulative acks.
• Unknown, duplicate and empty tokens.
• Late NOTIFY rewind and lower id with later changed_at.
• Abandoned sends, including the real LowWaterMarkTracker flush after Close.
• Saturation floor and a long node-drainer-style failure run.
• Checkpoint-write failure and retry.
• Concurrent delivery and ack.

Real PostgreSQL 16.15: a disposable container ran a scratch harness that is not committed. It drove the real watcher in polling and hybrid modes. A restart means a new watcher loading the durable token.

Scenario	This PR	main @ 8dbe1a1
Ack 1 of 5 buffered, restart	replays 2–5	replays nothing
Ack 3 of 5, restart	replays 4, 5	nothing
Watermark completions 3→1→2	correct at every step	loses events at steps 2 and 3
Lower id with later changed_at pending	held back	skipped
Late NOTIFY row below cursor pending	held back, replayed	skipped
Filtered tail, nothing pending	advances to cursor	same
Checkpoint write blocked by a lock	returns an error; next ack persists correctly	error swallowed, later save skips events
5,000-row backlog, every event acked	all delivered, no duplicates	same

Live suite: 19/19 pass on this PR. On main, 13 fail and 6 pass, as expected.

Throughput for the 5,000-row backlog, median of 3 runs:

Mode	This PR	main
Polling	8.41 s	8.21 s
Hybrid	8.27 s	8.16 s

That's 1–3% slower. A first version took the watcher lock twice per delivery and was 1.7x slower; it was fixed before this PR.

Commands:

• go test -race -count=3 ./pkg/datastore/providers/postgresql/... ./pkg/client/...: pass on macOS and in a Linux container.
• make -C store-client lint-test: pass, zero lint issues.
• make lint-test-all (macOS): stops only at the four syslog boot-ID tests, which need Linux /proc/sys/kernel/random/boot_id and are unrelated. Every earlier gate passes.
• No cluster E2E was run locally.

Checklist

• Self-review completed
• Documentation updated (if needed)
• Ready for review

Summary by CodeRabbit

• Bug Fixes
  • PostgreSQL change streams now preserve unacknowledged deliveries for replay, including after a restart or interrupted send.
  • Acknowledging a delivery also acknowledges earlier deliveries; acknowledgments no longer move the stream’s read position.
  • Checkpoint-save failures are reported, and delivery shutdown is coordinated to avoid interrupting an active send.
• Documentation
  • Clarified acknowledgment behavior, pending-delivery limits, replay, and checkpoint handling.

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[coderabbitai]

Walkthrough

The PostgreSQL change-stream watcher now tracks published deliveries separately from its read cursor and bounds saved checkpoints by outstanding deliveries. Acknowledgments apply cumulatively to tracked prefixes. Delivery and shutdown are serialized. Tests and documentation cover the acknowledgment contract, replay, checkpoint failures, and pending-delivery limits.

Changes: PostgreSQL Change-Stream Acknowledgments

Layer / File(s)	Summary
Acknowledgment contract and delivery state docs/postgresql-provider.md, store-client/pkg/client/interfaces.go, store-client/pkg/datastore/interfaces.go, store-client/pkg/datastore/providers/postgresql/changestream.go	Documentation defines cumulative acknowledgment behavior and caller requirements. The watcher adds bounded pending-delivery tracking, a delivery sequence, and an eviction floor.
Register and publish deliveries store-client/pkg/datastore/providers/postgresql/changestream.go, store-client/pkg/datastore/providers/postgresql/changestream_checkpoint_test.go	The watcher registers matching deliveries before publishing them and serializes sends with shutdown. Tests cover saturation, abandoned sends, replay, filtering, and concurrent delivery and acknowledgment.
Acknowledge prefixes and persist checkpoints store-client/pkg/datastore/providers/postgresql/changestream.go, store-client/pkg/datastore/providers/postgresql/changestream_checkpoint_test.go, store-client/pkg/datastore/providers/postgresql/changestream_resume_token_test.go, store-client/pkg/datastore/providers/postgresql/changestream_test.go	Acknowledgments remove the matching pending delivery and its prefix without advancing the read cursor. Checkpoints account for outstanding deliveries, and persistence failures are returned. Tests cover restart behavior, acknowledgment cases, and cursor preservation.

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

Change: Bug fix · Severity of issue fixed: Medium

Possibly related issues

• Issue 2348 concerns fault-remediation acknowledgments made out of delivery order. This PR documents the cumulative acknowledgment contract, but does not change the caller-side behavior identified in that issue.

Possibly related PRs

• NVIDIA/NVSentinel#2275: Both PRs change PostgreSQL change-stream delivery and coordinate access to delivery and read-cursor state.
• NVIDIA/NVSentinel#2250: Both PRs change PostgreSQL MarkProcessed validation and checkpoint persistence behavior.

Suggested labels: size/XL, area/core, area/docs

Suggested reviewers: saibernard, kaivalyamdabhadkar, cbumb, dims

Merge Risk: Minimal · up to eeb4c

The change fixes PostgreSQL change-stream checkpointing so a restart replays events that were delivered but not acknowledged. No actionable merge-blocking risk was identified in the supplied material.

Security architecture risk: Low · up to eeb4c

The change constrains checkpoint advancement and improves replay after restart without changing access permissions. Recovery still depends on consumers acknowledging a fully resolved delivery prefix, and end-to-end deployment and failure behavior was not fully validated.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• observed — The inspected persistence mutations remain a table-scoped processed-flag update and an upsert of the resume-token row identified by client_name. Pending-delivery state is local to each watcher; this PR does not change those database ownership keys or SQL predicates.

Trust Boundaries and Controls

• observed — A notification supplies a changelog identifier, while the event itself is fetched through a parameterized query constrained to the watcher's configured table. Acknowledgment tokens are parsed as integers; unmatched tokens cannot remove pending entries or advance the read cursor. Notification contents do not directly provide a persisted checkpoint position.

Resilience and Maintainability Implications

• inferred — Replay protection remains conditional on consumers resolving the entire acknowledged prefix. The unchanged node-drainer loop continues after preprocessing failures and can later acknowledge a subsequent event, so this watcher fix does not establish prefix completion for every consumer. That caller exposure predates the PR rather than constituting an introduced architecture concern.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title names the primary change: PostgreSQL change-stream checkpoints now save the acknowledged position instead of the read head. The changeset matches this. It adds delivery tracking, a checkpoin…
Linked Issues check		Directly linked issue #2288 has one coding objective: the saved PostgreSQL resume token must not pass a delivered but unacknowledged event, so restart redelivers it. The diff of store-client/pkg/datas…
Out of Scope Changes check		The changes in the reviewed diff fall into groups that support #2288's checkpoint fix: - Pending-delivery bookkeeping (pendingDelivery, pending, pendingFloor, pendingDeliveryLimit, registerDeliveryLo…
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.

Full details: Title check

Explanation

The title names the primary change: PostgreSQL change-stream checkpoints now save the acknowledged position instead of the read head. The changeset matches this. It adds delivery tracking, a checkpoint that cannot pass pending deliveries, cumulative acknowledgments, and no read-cursor advancement from acknowledgments. The title is specific and short, and it uses the same terms as the linked issue #2288.

Full details: Linked Issues check

Explanation

Directly linked issue #2288 has one coding objective: the saved PostgreSQL resume token must not pass a delivered but unacknowledged event, so restart redelivers it. The diff of store-client/pkg/datastore/providers/postgresql/changestream.go and the interface changes implement this:

1. Pending tracking before send (#2288): prepareDelivery registers each matching delivery (id, changed_at, seq) under mu before publishDelivery sends it on w.events. The read cursor is advanced in the same locked step.
2. Bounded save (#2288, #2265): checkpointPositionLocked starts at the read cursor and lowers it to (changed_at, id-1) for every pending delivery and for pendingFloor. Because it uses a strict predecessor at the same timestamp, a poll that resumes from the saved token includes the pending row again. Lower-id rows with later changed_at (#2265) and late NOTIFY rows below the cursor are covered, because the minimum is taken over all pending entries and not by id order.
3. Acks do not move the cursor: acknowledgeDeliveryLocked removes only the matched pending delivery and its prefix. Only reads advance lastEventID and highestReadEventID. An unknown token therefore cannot move the checkpoint past unread or pending rows.
4. Abandoned sends stay pending: publishDelivery returns nil on stopCh without removing the delivery, so a shutdown save does not certify an unsent row.
5. Checkpoint persistence errors are returned from MarkProcessed, so a failed save is not reported as success.

The issue's stated expected behavior is met for the watcher. The reviewed code shows the mechanism. I did not read the unit test files directly. The test coverage claims rely on the change summaries and the PR description. The live PostgreSQL harness is not committed, so its results cannot be checked from the repository.

Caveat: the cumulative MarkProcessed contract lets a caller that acks out of delivery order certify earlier unacknowledged deliveries. The PR documents two such callers, fault-remediation and node-drainer, as pre-existing caller behavior. Their follow-up issue references (#FRISSUE, #NDISSUE) are unfilled placeholders. This limit is on the caller side, and the watcher-side requirement of #2288 is satisfied.

Full details: Out of Scope Changes check

Explanation

The changes in the reviewed diff fall into groups that support #2288's checkpoint fix:

• Pending-delivery bookkeeping (pendingDelivery, pending, pendingFloor, pendingDeliveryLimit, registerDeliveryLocked, acknowledgeDeliveryLocked, checkpointPositionLocked): directly implements the saved-position bound.
• sendMu and closeOnce in Close, and the revised sendEventsToChannel: serialize delivery registration with Close so the events channel is not closed during a send. Required for the pending registration to be safe.
• timestampForAck and highestReadEventID changes: keep acks at or below the read high-water mark valid after purge. This follows from acks no longer moving the cursor.
• MarkProcessed error propagation: a failed checkpoint save now returns an error. This is part of the saved-position integrity that #2288 concerns. No caller source files in the reviewed diff were changed. Caller consequences depend on their existing error handling, which the PR describes but which I did not verify.
• Empty-token path: the legacy processed UPDATE at the read cursor is retained, and the change only removes the cursor-advance side effect.
• interfaces.go and interfaces.go (datastore) comment changes: document the cumulative MarkProcessed contract that the watcher now relies on.
• docs/postgresql-provider.md: documents the same contract.
• Test files (changestream_checkpoint_test.go, changestream_resume_token_test.go, changestream_test.go): cover the changed behavior. Their content was not read directly.

No change in the reviewed diff lacks a connection to the checkpoint behavior in #2288. The PR also reports a 1–3% throughput cost, which is a tradeoff of the same design and not an unrelated change.

Full details: Docstring Coverage

Explanation

Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 10 functions across 6 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

Finishing Touches

Generate unit tests (beta)

• Create a new PR

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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Failed pre-merge checks:
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Review info

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• Source mode: Auto
• Repository: NVIDIA/NVSentinel
• Branch: main
• File: .coderabbit.yaml
• Commit: 8dbe1a1
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Enterprise
• Run ID: 52ab6ef1-fc5b-408c-8b91-7600092306e4

Commits

Reviewing files that changed from the base of the PR and between 8dbe1a1 and eeb4cb0.

Files selected for processing: 7

• docs/postgresql-provider.md
• store-client/pkg/client/interfaces.go
• store-client/pkg/datastore/interfaces.go
• store-client/pkg/datastore/providers/postgresql/changestream.go
• store-client/pkg/datastore/providers/postgresql/changestream_checkpoint_test.go
• store-client/pkg/datastore/providers/postgresql/changestream_resume_token_test.go
• store-client/pkg/datastore/providers/postgresql/changestream_test.go

Included review availability: This review used your included allowance. Your plan provides up to 12 included reviews per hour; 11 remain after this review.

[sumedh-aerram]

Heads-up for review order: this conflicts with #2275 in changestream.go. Both change the NOTIFY and catch-up delivery path. #2275 is further along, so I'll rebase this onto it once it merges and rerun the real-PostgreSQL checks on the combined code. The pending-delivery bookkeeping here has to wrap #2275's catch-up lookups too.

I also updated the caller-audit section of the description after the discussion on #2348 and #2349: cold start covers both of those cases on restart.

@lalitadithya @KaivalyaMDabhadkar could one of you run /ok to test when you get a chance? CI hasn't run on this yet, and I'd like to catch anything platform-specific before the rebase.