storelimit: support inbound leader transfer rate limiting - #11197
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Limit leader transfers into hot stores to reduce cache warm-up I/O spikes. Reuse the v1 per-store token buckets with a fixed per-transfer cost, and expose the limit through the existing API and PD Control paths. Signed-off-by: JmPotato <github@ipotato.me>
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Included review availability: Your plan provides up to 4 included reviews per hour; 3 remain after this review. 📝 WalkthroughWalkthroughThe PR adds the ChangesInbound leader transfer limits
Estimated code review effort: 4 (Complex) | ~45 minutes Sequence Diagram(s)sequenceDiagram
participant PDControl
participant StoreLimitAPI
participant ScheduleConfig
participant StoreStateFilter
participant TransferLeaderOperator
PDControl->>StoreLimitAPI: Set transfer-leader-in rate
StoreLimitAPI->>ScheduleConfig: Validate and persist rate
TransferLeaderOperator->>StoreStateFilter: Check target store
StoreStateFilter->>ScheduleConfig: Read configured rate
StoreStateFilter-->>TransferLeaderOperator: Allow or throttle transfer
Merge Risk: 🟡 Moderate · up to This change adds inbound leader-transfer limiting, but users cannot configure the documented unlimited value through the HTTP API or PD Control, and its unlimited transition coverage is incomplete. Resolve these configuration and validation issues before merging. 🚥 Pre-merge checks | ✅ 3 | ❌ 2❌ Failed checks (2 warnings)
✅ Passed checks (3 passed)
Full details: Linked Issues checkExplanation The implementation satisfies the linked issue objectives for inbound-only limiting, fixed target-store cost, per-store and all-store configuration, filtering, controller enforcement, field preservation, API and PD Control support, tests, and E2E coverage. However, the linked issue requires a default value of 0 meaning unlimited, while this pull request uses storelimit.Unlimited as the default and migrates legacy zero values to it. Resolution Either retain 0 as the default representation for TransferLeaderIn while preserving unlimited behavior, or update the linked issue and acceptance criteria to explicitly allow storelimit.Unlimited as the default and document the zero-value migration behavior.
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Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
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Inline comments:
In `@pkg/schedule/filter/filters_test.go`:
- Around line 331-332: Refresh the store’s StoreRateLimit to rate 0 after
SetStoreLimit and before asserting filter.Target, so exceedTransferLeaderInLimit
evaluates the zero-rate behavior with matching limiter state rather than using
the stale-rate bypass.
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pkg/core/storelimit/limit.gopkg/core/storelimit/limit_test.gopkg/core/storelimit/store_limit.gopkg/mcs/scheduling/server/cluster.gopkg/mcs/scheduling/server/config/config.gopkg/mcs/scheduling/server/config/config_test.gopkg/schedule/config/config.gopkg/schedule/config/config_test.gopkg/schedule/filter/counter.gopkg/schedule/filter/filters.gopkg/schedule/filter/filters_test.gopkg/schedule/filter/status.gopkg/schedule/operator/operator_controller_test.gopkg/schedule/operator/operator_test.gopkg/schedule/operator/step.gopkg/schedule/operator/step_test.gopkg/schedule/plan/status.gopkg/statistics/store_collection.gopkg/statistics/store_collection_test.goserver/api/config_test.goserver/api/store.goserver/cluster/cluster.goserver/cluster/cluster_test.goserver/cluster/scheduling_controller.goserver/config/config_test.goserver/config/persist_options.gotests/integrations/mcs/scheduling/server_test.gotools/pd-ctl/pdctl/command/store_command.gotools/pd-ctl/tests/store/store_test.go
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| opt.SetStoreLimit(store.GetID(), storelimit.TransferLeaderIn, 0) | ||
| re.Equal(plan.StatusOK, filter.Target(opt, store).StatusCode) |
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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win
Refresh the store limiter before asserting the zero-limit case.
opt.SetStoreLimit changes the configured rate, but the StoreRateLimit in store remains exhausted at ratePerSec. The rate mismatch makes exceedTransferLeaderInLimit return StatusOK through its stale-rate bypass before checking availability. Refresh the limiter to rate 0 so this assertion covers the zero-rate unlimited behavior.
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In `@pkg/schedule/filter/filters_test.go` around lines 331 - 332, Refresh the
store’s StoreRateLimit to rate 0 after SetStoreLimit and before asserting
filter.Target, so exceedTransferLeaderInLimit evaluates the zero-rate behavior
with matching limiter state rather than using the stale-rate bypass.
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Defer the builder's transfer-in budget check to operator admission, where the final priority is known. Keep scheduler prefiltering and all other target checks unchanged. Cover urgent evacuation and ordinary admission with exhausted targets, and ensure skipping the budget check does not allow disconnected stores. Signed-off-by: JmPotato <github@ipotato.me>
Signed-off-by: JmPotato <github@ipotato.me>
| // DefaultTiFlashStoreLimit is the default TiFlash store limit of add peer and remove peer. | ||
| DefaultTiFlashStoreLimit = StoreLimit{AddPeer: 30, RemovePeer: 30} | ||
| // DefaultStoreLimit is the default store limit. | ||
| DefaultStoreLimit = StoreLimit{AddPeer: 15, RemovePeer: 15, TransferLeaderIn: 0} |
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It's better to keep the same semantics.
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Agreed, addressed in f72a06c.
- All three types now share the same pd-ctl syntax and positive, finite rate validation. The transfer-leader-in-specific zero exception is removed.
- TransferLeaderIn defaults to the existing
storelimit.Unlimited(100000000), which also restores unlimited transfers. Legacy omitted/zero values are normalized on config load; shared limiter behavior is unchanged. - The pd-ctl
allsafety cap now acceptsUnlimitedfor all three types, not just leader transfers. Omitting the type still updates only AddPeer/RemovePeer for compatibility.
The intentional differences are the default (unlimited to preserve existing leader scheduling) and fixed per-transfer cost, independent of region size. Configuration/reload tests and real-process limited-to-Unlimited transitions passed in both classic PD and independent scheduling deployments.
Signed-off-by: JmPotato <github@ipotato.me>
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Inline comments:
In `@server/api/store.go`:
- Line 757: Restore zero as the unlimited rate for transfer-leader-in while
continuing to reject negative, NaN, and infinite values. In
server/api/store.go:757, make validation type-aware; update
server/api/store_test.go:37-39 to assert zero succeeds for transfer-leader-in.
Apply the same type-aware validation in
tools/pd-ctl/pdctl/command/store_command.go:566, :602, and :698 for individual,
simple all-store, labeled all-store, and deprecated all-store commands. Update
tools/pd-ctl/tests/store/store_test.go:148-149 and :163-164 to expect zero to
configure transfer-leader-in limits.
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pkg/mcs/scheduling/server/config/config_test.gopkg/schedule/config/config.gopkg/schedule/config/config_test.gopkg/schedule/filter/filters_test.goserver/api/config_test.goserver/api/store.goserver/api/store_test.goserver/cluster/cluster_test.goserver/config/config_test.gotests/integrations/mcs/scheduling/server_test.gotools/pd-ctl/pdctl/command/store_command.gotools/pd-ctl/tests/store/store_test.go
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- server/cluster/cluster_test.go
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Signed-off-by: JmPotato <github@ipotato.me>
Initialize missing transfer-leader-in fields from the configured default while preserving explicitly configured values. Signed-off-by: JmPotato <github@ipotato.me>
Resolve operator priority before leader target selection and pass it through StoreStateFilter to the resulting operator. Preserve urgent evacuation and health checks without a separate transfer-in skip flag. Cover early checker and scheduler selection, explicit priority overrides, and preservation of unrelated store limits in scheduling service tests. Signed-off-by: JmPotato <github@ipotato.me>
Keep leader target filtering independent of operator priority, including Builder validation. Preserve existing controller admission and explicit filter bypass behavior, and document the boundary for future review. Restore the existing operator priority assignment flow and cover exhausted limits for admin construction, evacuation, witness and fast failover. Signed-off-by: JmPotato <github@ipotato.me>
Keep the server-side leader transfer limit change independent of PD Control help, validation and integration tests. Submit the CLI adaptation separately after the server feature is merged. Signed-off-by: JmPotato <github@ipotato.me>
Signed-off-by: JmPotato <github@ipotato.me>
Reserve a full inbound leader cost for each distinct candidate and the compatibility target, since TiKV chooses the actual receiver. Preserve multi-target execution at the cost of conservative budget consumption. Signed-off-by: JmPotato <github@ipotato.me>
Fill missing per-store transfer-leader-in fields during schedule JSON decoding so generic configuration updates inherit the configured default. Reuse the same adjustment after persisted defaults are migrated, while preserving explicitly supplied values. Signed-off-by: JmPotato <github@ipotato.me>
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/retest |
Match the TiFlash store-limit assertion to the Unlimited inbound leader transfer default, preserving the explicit 30/min peer limits. Signed-off-by: JmPotato <github@ipotato.me>
| to.LeaderCount++ | ||
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| // TiKV chooses the receiver, so reserve a full cost for every possible target. | ||
| to.AddStepCost(storelimit.TransferLeaderIn, storelimit.RegionInfluence[storelimit.TransferLeaderIn]) |
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[P1] Charge only the actual receiver. ToStores is the fallback set sent to TiKV, but one store receives the leader. The controller consumes every StepCost, and the v1 Ack path does not return tokens. evict-leader passes every eligible follower as a candidate, so one successful transfer consumes the inbound budget of stores that never received a leader and then throttles later balance-leader work. Please either use one target while this limit is enabled, or account for the selected receiver only.
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For this inbound-throttling feature, I prefer to retain conservative accounting: charge each distinct possible target, including the compatibility target, because TiKV chooses the receiver after PD admits the operator.
This intentionally consumes budget on candidates that do not ultimately receive the leader and can slow subsequent scheduling to those stores. I consider that an acceptable trade-off here. It preserves TiKV's multi-target selection while accounting for every possible destination in advance, without adding a reservation/refund lifecycle. I'll keep the current approach in this PR.
| return limit.AddPeer | ||
| case storelimit.RemovePeer: | ||
| return limit.RemovePeer | ||
| case storelimit.TransferLeaderIn: |
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[P1] Refresh existing MCS store limiters when scheduling config changes. The MCS config watcher replaces ScheduleConfig but does not update the limiter stored in existing StoreInfo instances, which start as unlimited. Normal admission eventually calls getOrCreateStoreLimit, but evict-leader is Urgent and skips that path, then consumes the stale unlimited limiter. A newly configured transfer-leader-in limit therefore does not constrain urgent leader eviction in the independent scheduling deployment. Refresh live limiters on config updates, or refresh from PersistConfig before this filter checks availability.
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Agreed that configuration updates need to synchronize the live limiters. This is tracked separately in #11201, covering the shared mechanism for AddPeer, RemovePeer, and TransferLeaderIn, including recovery after raising an exhausted low-rate limit. I'll leave that fix to the follow-up issue.
| // including when this filter is used by Builder. Controller admission retains its | ||
| // existing Urgent exemption; passing this filter does not reserve tokens. | ||
| // TODO: Reconcile leader-transfer priorities with store-limit admission semantics. | ||
| if !f.AllowTemporaryStates && !store.IsAvailable(storelimit.TransferLeaderIn, f.OperatorLevel) { |
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[P1] Define one priority policy for this limit. Controller admission explicitly lets Urgent operators bypass store-limit checks, while this target filter rejects an Urgent candidate when its budget is exhausted. An evict-leader operation can therefore be rejected before admission, yet proceed when the same limit is exhausted after selection. The TODO documents the conflict but leaves user-visible behavior dependent on timing. Please apply one policy consistently in target selection and admission.
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The priority interaction is intentionally unchanged in this PR. Target selection checks the budget, while Controller admission retains the existing Urgent exemption. An urgent transfer can therefore proceed if the budget is exhausted after selection; the observed evict behavior is expected under this policy. Unifying target selection and admission priorities is outside this PR's scope.
| // SendSnapshot indicates the type of sending snapshot. | ||
| SendSnapshot | ||
| // TransferLeaderIn indicates the limit for leaders transferred into a store. | ||
| TransferLeaderIn |
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[P2] This new limit is ineffective with store-limit-version=v2. SlidingWindows returns available and consumes no token for every type other than SendSnapshot, and the store-limit update APIs reject v2. As a result TransferLeaderIn can be present in configuration but never throttles under v2. Please implement the type in the v2 limiter, or explicitly limit and document this feature as v1-only.
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Yes, transfer-leader-in is v1-only at this stage, as described in the PR. The existing v2 pass-through behavior for non-SendSnapshot types remains unchanged. Implementing this limit for v2 is outside this PR's scope.
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| to.LeaderCount++ | ||
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| // TiKV chooses the receiver, so reserve a full cost for every possible target. | ||
| to.AddStepCost(storelimit.TransferLeaderIn, storelimit.RegionInfluence[storelimit.TransferLeaderIn]) |
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Empty regions pay the full TransferLeaderIn cost here, unlike AddPeer/RemovePeer.
This calls AddStepCost unconditionally with the fixed RegionInfluence[TransferLeaderIn] cost, regardless of region size. AddPeer/RemovePeer instead go through AdjustStepCost, which is free at or below EmptyRegionApproximateSize and discounted below SmallRegionThreshold.
Since this limit's stated goal is cache warm-up I/O, which scales with the region's actual data, a region at/near EmptyRegionApproximateSize has little to no block cache to warm up and arguably shouldn't consume the transfer-in budget — freshly split/created regions are commonly near-empty, so this can throttle harmless leader placement toward them.
Would it make sense to route this through AdjustStepCost (with a TransferLeaderIn entry in SmallRegionInfluence) for consistency with AddPeer/RemovePeer, or is charging leader transfers independent of region size intentional even for empty regions?
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I think this is a reasonable consideration. For the current use case, though, a simple fixed cost is sufficient. We can revisit size-aware costs as a future improvement, but I'd prefer to keep this PR's logic simple and effective, especially since we plan to deliver it to a customer as a hotfix.
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/retest |
| if !isStoreLimitRateValid(c.DefaultStoreLimit.TransferLeaderIn) { | ||
| return errors.New("default-store-limit.transfer-leader-in should be finite and non-negative") | ||
| } | ||
| for storeID, limit := range c.StoreLimit { |
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This per-store validation only covers TransferLeaderIn, not AddPeer/RemovePeer.
Before this PR, Validate() never checked per-store StoreLimit entries at all (only the DefaultStoreLimit globals). This loop is new and only guards the new field, so a NaN/Inf/negative value can still reach limit.AddPeer or limit.RemovePeer for an individual store through any path that bypasses the dedicated HTTP rate validation (e.g. a generic POST /pd/api/v1/config update decoded straight into ScheduleConfig). A negative rate reaching StoreRateLimit.limit.Reset would feed ratelimit.NewRateLimiter a negative rate, which is unspecified behavior for the underlying limiter.
Since all three types share the same StoreLimitConfig struct and isStoreLimitRateValid, would it make sense to validate AddPeer/RemovePeer here too while this loop already exists, rather than leaving TransferLeaderIn as the only protected type?
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Fixed in ffe2311. The per-store loop now validates AddPeer and RemovePeer with the same finite, non-negative check as TransferLeaderIn. Zero remains valid in schedule configuration.
Added regression coverage for all three fields, including negative values, NaN, ±Inf, zero, and valid rates. Both configuration HTTP endpoints are tested to reject negative rates without changing in-memory or persisted configuration. The targeted tests pass in Classic and NextGen builds, along with the full configuration integration suite and related package basic tests.
Signed-off-by: JmPotato <github@ipotato.me>
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/retest |
| // including when this filter is used by Builder. Controller admission retains its | ||
| // existing Urgent exemption; passing this filter does not reserve tokens. | ||
| // TODO: Reconcile leader-transfer priorities with store-limit admission semantics. | ||
| if !f.AllowTemporaryStates && !store.IsAvailable(storelimit.TransferLeaderIn, f.OperatorLevel) { |
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After an exhausted v1 transfer-leader-in bucket is raised through the generic schedule-config endpoint, the persisted rate changes but this pre-admission check continues to read the stale StoreInfo limiter. It rejects the target before Controller.getOrCreateStoreLimit can refresh the rate, so this advertised update path can leave leader scheduling blocked indefinitely in production.
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This is the same configuration-to-limiter synchronization issue we discussed earlier and tracked in #11201. The generic schedule-config endpoint is another trigger: the configuration changes, but target selection still reads the stale limiter before the Controller can refresh it.
As agreed, we'll keep this fix separate from this PR and address it through the shared synchronization mechanism. That work is being developed independently in #11214; the TransferLeaderIn refresh coverage will remain part of the follow-up.
| } | ||
| for storeID, limitFields := range fields.StoreLimit { | ||
| if _, defined := limitFields["transfer-leader-in"]; !defined { | ||
| c.StoreLimit[storeID] = c.StoreLimit[storeID].SetLimit(storelimit.TransferLeaderIn, c.DefaultStoreLimit.TransferLeaderIn) |
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When a legacy client updates an existing store through either generic config endpoint with only add-peer and remove-peer, this decoder replaces that store's finite transfer-leader-in override with DefaultStoreLimit.TransferLeaderIn (normally Unlimited). A routine peer-limit update can therefore silently disable inbound-leader throttling and reintroduce the cold-store I/O spike this feature is intended to prevent.
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Fixed in dce767c82c. Both generic configuration endpoints now merge updates into the existing per-store limits, so a legacy peer-only update preserves the current transfer-leader-in value. New stores inherit defaults from the same request, independently of field/map ordering. Legacy snapshot migration, explicit zero, null, and case-insensitive JSON fields are also covered.
Added unit, persistence/reload, concurrent-update, and HTTP integration tests. Classic/NextGen and race/deadlock checks passed; the new regressions fail against the previous implementation. Fresh real-cluster E2E passed in all four Community/TiDB X × standalone/microservice deployments: 220 configuration checks, 12 rolling-restart/leader-return cycles, and 453,542 SQL requests with zero errors. The old-client requests were also exercised immediately before deleting Evict in every cycle.
The runtime limiter-refresh issue remains separate in #11201 / #11214.
Merge per-store JSON updates into existing limits so legacy peer-only requests retain inbound leader limits. Initialize new stores from the defaults in the same request and apply schedule fields atomically. Preserve legacy snapshot migration semantics, explicit zero values, null fields, and case-insensitive JSON decoding. Cover persistence, concurrent updates, and both generic configuration endpoints. Signed-off-by: JmPotato <github@ipotato.me>
Reuse the existing HTTP rate validation and remove its redundant helper and helper-only test. JSON decoding already rejects non-finite numbers. Read per-store entries alongside default limits during snapshot migration to avoid decoding the same document twice while preserving legacy defaults. Signed-off-by: JmPotato <github@ipotato.me>
Allocate store limits only when a non-null JSON object is provided. Keep omitted and null maps nil on zero-value configs used by tools, while preserving explicit empty objects and existing store entries. Cover map presence and partial updates in the existing regression suite. Signed-off-by: JmPotato <github@ipotato.me>
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: bufferflies, niubell, rleungx, YuhaoZhang00 The full list of commands accepted by this bot can be found here. The pull request process is described here DetailsNeeds approval from an approver in each of these files:
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6 participants
What problem does this PR solve?
Control leader return after removing evict-leader during TiKV rolling restarts,
to limit cache warm-up I/O pressure.
Issue Number: Close #11196
What is changed and how does it work?
PD Control command adaptation and its tests are in #11200, which must merge
after this PR. This PR contains the server-side implementation only.
Check List
Tests
JSON map presence regression (d6859b9b2f): Omitted or null
store-limitremains nil when decoding into a zero-value configuration; explicit empty objects and existing store entries are preserved. New regression cases fail before the fix. Classic/NextGen pd-backup and pd-ctl Config suites, configuration packages, and configuration HTTP integration tests passed; incremental lint passed.On Go 1.27.1, all tests in 10 relevant packages passed with both Classic and NextGen builds: store limits, filters, operators, schedulers, checkers, scatter, schedule configuration, statistics, server configuration, and scheduling-service configuration.
The pd-ctl Store suite, MCS StoreLimit integration tests in both builds, scheduler
basic-test, and additional local budget-exhaustion/recovery tests passed. Full repository CI was not run as part of this validation.Per-store rate validation (ffe2311456, Go 1.27.0): Classic/NextGen regression tests and the full configuration integration suite passed. Tests cover negative/non-finite rates, valid zero/finite/Unlimited values, and rejection through both configuration HTTP endpoints with in-memory and persisted configuration unchanged. Related package
basic-testand incremental lint passed.make checkis blocked by existing findings in unrelated files under the Go 1.27-compatible linter.Configuration compatibility regression (dce767c82c, Go 1.27.0): Classic/NextGen unit and HTTP integration tests, concurrent-update race/deadlock tests, and incremental lint passed. Covers legacy peer-only and leader-only requests, explicit zero/finite/Unlimited values, null and case-insensitive fields, default/new-store updates in one request, persistence/reload, scheduling-service configuration, and rejected batches leaving schedule configuration unchanged. New regression tests fail against the previous implementation.
Local configuration and rolling-restart E2E (2026-09-10)
Tested the source in dce767c82c with pd-ctl from #11200 (
c0c2a76e21fe8e8120637ef05397ddebb5a57869). Fresh Community TiKV/TiDB and TiDB X/CSE deployments each use standalone PD or independent API + TSO + scheduling services, with scheduling fallback disabled.Each deployment has three stores, three replicas, 3,000 user regions, 300,000 rows, and continuous point reads and multi-key writes. The configuration checks exercise both generic HTTP endpoints and restart PD plus the scheduling service where applicable to verify persisted limits. Each rolling cycle uses pd-ctl to set Unlimited, 300/min, or 600/min; evicts leaders to zero; restarts TiKV; confirms Evict still prevents leader return; issues legacy peer-only updates through both configuration endpoints; and deletes Evict to observe ordinary balance-leader return.
All 220/220 configuration checks and 12/12 rolling cycles passed. Sustained rates from actual TiKV leader transitions:
Unlimited controls reached approximately 369–374 leaders/s. TiKV transitions matched ordinary balance-leader operators and were cross-checked against TiKV and PD/scheduling gauges. All 453,542 workload SQL requests succeeded. Every store passed a 20-second error-free read/write recovery window with p99 ≤ 1s before the next cycle.
Real-cluster grant-leader and shuffle-leader checks at 60/min measured approximately 1 leader/s per target. evict-leader slowed down but reached up to 1.43 leaders/s over a 35-second window, as expected with the retained Urgent admission exemption. v2 Store limit and Raft's own elections remain outside this limit.
These checks cover legacy-format requests/snapshots and same-version process restarts. Mixed-version PD upgrades/downgrades, production cold-storage pressure, and service failover were not tested. Old PD binaries can still drop fields they do not recognize when writing full configuration snapshots. Runtime configuration-to-limiter refresh remains tracked separately by #11201 and #11214. Other schedulers retain their existing unit-test coverage.
Code changes
Release note
Summary by CodeRabbit
New Features
transfer-leader-instore limits across the API, persistence, and monitoring.Bug Fixes