logpuller: send CDC scan priority

[hongyunyan]

Background

TiCDC creates different kinds of log puller region tasks. Bootstrap scans for newly created changefeeds should not have the same downstream scan priority as repair or retry scans that affect existing changefeed lag.

Motivation

Propagating scan priority through ChangeDataRequest lets CSE protect high-priority CDC scans while scheduling new changefeed bootstrap scans as low priority.

Summary

• Map log puller task types to cdcpb.ScanPriority.
• Set ChangeDataRequest.ScanPriority when building CDC requests.
• Preserve request priority across busy and congested retry paths.
• Add focused tests for task priority mapping, request construction, and retry behavior.
• Update github.com/pingcap/kvproto to the protocol branch pseudo-version.
• Merge the latest master and preserve event store changefeed IDs when creating log puller subscriptions.

Dependencies

• Protocol PR: cdcpb: add CDC scan priority kvproto#1493

Validation

• go mod tidy
• make fmt
• make cdc
• NEXT_GEN=1 make cdc
• go test ./logservice/eventstore ./logservice/logpuller
• tools/bin/golangci-lint run --timeout 10m0s --new-from-rev=2258270f041a2267ede73126a033f889f4d51632

Summary by CodeRabbit

• New Features
  • Added configuration option old-start-ts-scan-low-priority-threshold (default: 30m) to influence initial scan priority.
  • Introduced scan-priority mapping (high/low) with unknown priorities normalized to low, plus realtime scan priority that upgrades region/range work to high after the subscription catches up.
  • Updated dashboards to include additional scan scheduler queue/running/latency panels and descriptions.
• Bug Fixes
  • Improved retry scheduling to preserve the original scan priority and use the correct priority source for retried work.
  • Enhanced warnings and subscription/dispatch logs with changefeed identifiers and priority context.
• Tests
  • Added unit tests for scan-priority mappings, request priority behavior, and realtime retry upgrades.
• Chores
  • Updated the kvproto dependency.

[ti-chi-bot]

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📝 Walkthrough

Walkthrough

This PR adds scan-priority scheduling in logpuller, threads changefeedID through subscription call paths, introduces a configurable old-start-ts threshold, and updates request creation, retry handling, tests, and Grafana dashboards to carry scan-priority metadata.

Changes

Scan Priority Scheduling and ChangefeedID Threading

Layer / File(s)	Summary
Priority mapping and config go.mod, logservice/logpuller/priority_task.go, logservice/logpuller/priority_task_test.go, pkg/config/debug.go, logservice/logpuller/region_state.go, logservice/logpuller/region_req_cache_test.go	Bumps kvproto, adds TaskType ↔ cdcpb.ScanPriority helpers and tests, introduces the old-start-ts threshold config, and stores scan priority on region state.
Subscription client priority flow logservice/logpuller/subscription_client.go, logservice/logpuller/region_event_handler.go	Adds changefeedID and realtime scan priority state, computes initial task priority, enables realtime priority after catch-up, and derives retry priority from prior scan priority.
Region request propagation logservice/logpuller/region_request_worker.go, logservice/logpuller/region_request_worker_test.go	Carries normalized scan priority into outgoing region requests and updates the request builder test.
ChangefeedID call-site updates logservice/eventstore/event_store.go, logservice/eventstore/event_store_test.go, logservice/schemastore/ddl_job_fetcher.go	Threads changefeedID through dispatcher registration and subscription call sites, updates the mock signature, and formats the DDL subscription name.
Scan-priority and call-path tests logservice/logpuller/subscription_client_test.go	Updates existing tests for the new signatures and adds coverage for scan-priority mapping, retry preservation, initial priority selection, and realtime priority upgrades.
Grafana scan scheduler panels metrics/grafana/ticdc_new_arch.json, metrics/nextgengrafana/ticdc_new_arch_next_gen.json	Adds CDC scan scheduler panels, descriptions, PromQL targets, and layout shifts in both dashboard JSON files.

Estimated code review effort: 4 (Complex) | ~60 minutes

Possibly related PRs

• pingcap/ticdc#4507: Also updates the Grafana dashboard JSON layout and panel positioning.

Suggested reviewers: lidezhu, asddongmen

Sequence Diagram(s)

sequenceDiagram
  participant RegionEventHandler
  participant SubscriptionClient
  participant RegionRequestWorker
  participant cdcpb.ChangeDataRequest

  RegionEventHandler->>SubscriptionClient: maybeEnableRealtimeScanPriority(span, resolvedTs)
  SubscriptionClient->>SubscriptionClient: newSubscribedSpan(changefeedID, ...)
  SubscriptionClient->>SubscriptionClient: initial priority + effectiveScanTaskPriority
  SubscriptionClient->>RegionRequestWorker: scheduleRegionRequest / scheduleRangeRequest
  RegionRequestWorker->>cdcpb.ChangeDataRequest: createRegionRequest(ScanPriority)
  SubscriptionClient->>SubscriptionClient: doHandleError(retryPriority)

Loading

Poem

A rabbit hops where priorities glow,
High and low in a tidy row.
ChangefeedID jingles along the track,
Realtime wakes when scans come back.
🐇✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers the change, but it does not follow the required template and is missing the issue number, checklist, questions, and release note.	Add the required sections: What problem does this PR solve?, Issue Number, What is changed and how it works?, Tests, Questions, and Release note.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately reflects the main logpuller change to send scan priority.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[gemini-code-assist]

Code Review

This pull request updates the kvproto dependency and introduces support for preserving scan priority across retries when handling congested or busy server errors in logpuller. It adds mapping utilities between TaskType and cdcpb.ScanPriority, stores the scan priority in regionInfo, and ensures it is propagated and maintained during retries. Comprehensive unit tests are also added to verify these mappings and retry behaviors. I have no feedback to provide.

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[coderabbitai]

🧹 Nitpick comments (1)

logservice/logpuller/subscription_client_test.go (1)

537-731: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Well-structured coverage of scan-priority behavior; minor duplication across new tests.

Assertions for TestInitialScanTaskPriority, TestSubscribeUsesInitialScanTaskPriority, TestRealtimeScanPriorityEnabledAfterSubscriptionCatchesUp, and the retry-upgrade tests all match the priority computation/upgrade logic shown in subscription_client.go (initialScanTaskPriority, maybeEnableRealtimeScanPriority, effectiveScanTaskPriority, doHandleError).

The rawSpan/subscribedSpan/regionInfo construction block (Lines 406-417, 480-491, 666-678, 695-707) is duplicated near-verbatim across four test functions. Consider extracting a small helper (e.g. newTestRegionWithScanPriority(t, subID, priority)) to reduce duplication and ease future maintenance.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@logservice/logpuller/subscription_client_test.go` around lines 537 - 731, The
new scan-priority tests repeat the same raw span, subscribed span, and region
setup in several places, so factor that shared construction into a small helper
to keep the tests maintainable. Extract the repeated setup around
TestInitialScanTaskPriority, TestSubscribeUsesInitialScanTaskPriority,
TestRealtimeScanPriorityEnabledAfterSubscriptionCatchesUp, and the retry-upgrade
tests into a helper such as newTestRegionWithScanPriority or
newTestSubscribedSpan, then reuse it while keeping each test focused on its
specific priority assertion.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@logservice/logpuller/subscription_client_test.go`:
- Around line 537-731: The new scan-priority tests repeat the same raw span,
subscribed span, and region setup in several places, so factor that shared
construction into a small helper to keep the tests maintainable. Extract the
repeated setup around TestInitialScanTaskPriority,
TestSubscribeUsesInitialScanTaskPriority,
TestRealtimeScanPriorityEnabledAfterSubscriptionCatchesUp, and the retry-upgrade
tests into a helper such as newTestRegionWithScanPriority or
newTestSubscribedSpan, then reuse it while keeping each test focused on its
specific priority assertion.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 2d06ba2b-1f41-4995-9b2f-4421ea62b717

📥 Commits

Reviewing files that changed from the base of the PR and between 2258270 and 3a26268.

⛔ Files ignored due to path filters (1)

• go.sum is excluded by !**/*.sum

📒 Files selected for processing (14)

• go.mod
• logservice/eventstore/event_store.go
• logservice/eventstore/event_store_test.go
• logservice/logpuller/priority_task.go
• logservice/logpuller/priority_task_test.go
• logservice/logpuller/region_event_handler.go
• logservice/logpuller/region_req_cache_test.go
• logservice/logpuller/region_request_worker.go
• logservice/logpuller/region_request_worker_test.go
• logservice/logpuller/region_state.go
• logservice/logpuller/subscription_client.go
• logservice/logpuller/subscription_client_test.go
• logservice/schemastore/ddl_job_fetcher.go
• pkg/config/debug.go

[coderabbitai]

🧹 Nitpick comments (1)

metrics/grafana/ticdc_new_arch.json (1)

22661-22745: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Minor: count-panel Y-axis format inconsistent with similar panels.

Queue Length and Running panels use "format": "none" for the count axis, whereas a similar counter panel ("Unresolved Region Request Count") uses "format": "short". Purely cosmetic.

Also applies to: 22746-22851

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@metrics/grafana/ticdc_new_arch.json` around lines 22661 - 22745, The count
panel’s Y-axis formatting is inconsistent with the similar counter panel; in the
Grafana panel definition for CDC Scan Scheduler Queue Length (and the matching
panel referenced by the review), update the first yaxes entry to use the same
count format as the “Unresolved Region Request Count” panel. Keep the change
limited to the panel JSON around the graph configuration so the axis formatting
is consistent across these related panels.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@metrics/grafana/ticdc_new_arch.json`:
- Around line 22661-22745: The count panel’s Y-axis formatting is inconsistent
with the similar counter panel; in the Grafana panel definition for CDC Scan
Scheduler Queue Length (and the matching panel referenced by the review), update
the first yaxes entry to use the same count format as the “Unresolved Region
Request Count” panel. Keep the change limited to the panel JSON around the graph
configuration so the axis formatting is consistent across these related panels.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 74ff9c3c-9edc-4e41-9170-adba50fb17c8

📥 Commits

Reviewing files that changed from the base of the PR and between ab05078 and 0d7ab0b.

📒 Files selected for processing (4)

• logservice/logpuller/region_request_worker.go
• logservice/logpuller/region_request_worker_test.go
• metrics/grafana/ticdc_new_arch.json
• metrics/nextgengrafana/ticdc_new_arch_next_gen.json

💤 Files with no reviewable changes (2)

• logservice/logpuller/region_request_worker_test.go
• logservice/logpuller/region_request_worker.go