ddl, br: gate adding tiflash replica by global variable - #70500
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Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review. 📝 WalkthroughWalkthroughThe change adds the ChangesColumnar Storage and TiFlash Replica Management
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🔵 Low · up to The PR changes when TiFlash replica metadata can be created, while the remaining bounded risks are inaccurate design documentation and a POST test that may not detect a method-guard regression; the change is mergeable with explicit owner follow-up on these items. Sequence Diagram(s)sequenceDiagram
participant Client
participant HTTPHandler
participant Domain
participant InfoSchema
participant GlobalVariables
Client->>HTTPHandler: GET /tiflash/replica
HTTPHandler->>Domain: Reload latest schema
Domain-->>HTTPHandler: InfoSchema
HTTPHandler->>InfoSchema: Count TiFlash-attributed tables
HTTPHandler->>GlobalVariables: Read columnar-storage status
GlobalVariables-->>HTTPHandler: Enabled or disabled
HTTPHandler-->>Client: FlashReplicaSummary
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Suggested reviewers: Poem
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In `@docs/design/2026-08-13-tiflash-on-demand-ddl-gate-global-variable.md`:
- Around line 371-373: Update the design document’s write-permission test
location from pkg/executor to pkg/privilege/privileges/privileges_test.go, where
the SEM v2 coverage is implemented.
- Around line 4-5: Replace the placeholder XXX URLs in the Discussion PR and
Tracking Issue entries with valid references, or remove those entries if the
corresponding PR and issue do not yet exist.
- Around line 176-179: Replace the invalid combined SQL value notation with
valid single-value substitution in both occurrences of the control-plane
command: docs/design/2026-08-13-tiflash-on-demand-ddl-gate-global-variable.md
lines 176-179 and 325-326. Use separate ON/OFF commands or one placeholder
representing either value; update both locations consistently.
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docs/design/2026-08-13-tiflash-on-demand-ddl-gate-global-variable.mdpkg/ddl/create_table.gopkg/ddl/ddl_tiflash_api.gopkg/ddl/executor.gopkg/ddl/index_modify_test.gopkg/ddl/table.gopkg/ddl/tiflash_replica_test.gopkg/meta/model/job_args.gopkg/meta/model/job_args_test.gopkg/privilege/privileges/privileges_test.gopkg/sessionctx/vardef/tidb_vars.gopkg/sessionctx/variable/sysvar.gopkg/util/dbterror/ddl_terror.go
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Gate count>0 replica DDL on tidb_columnar_storage_enabled so Premium columnar clusters fail fast instead of silently creating unready replicas. Signed-off-by: JaySon-Huang <tshent@qq.com>
…e is disabled Stop copying or auto-creating TiFlash replica metadata on CREATE TABLE / LIKE, and fail ADD/CREATE columnar index, so the gate cannot be bypassed when Columnar Storage is off. Signed-off-by: JaySon-Huang <tshent@qq.com>
Signed-off-by: JaySon-Huang <tshent@qq.com>
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Signed-off-by: JaySon-Huang <tshent@qq.com>
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Give cluster operators a fail-closed count of live logical tables with TiFlash replica metadata before disabling columnar storage.
Keep GET /tiflash/replica as the live summary, document why Reload must run first, and drop the design doc now that the contract lives in the HTTP API docs.
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/retest |
Keep stripping TiFlash replicas on Next-Gen snapshot restore, and log tidb_columnar_storage_enabled from the BR Domain sysvar cache for diagnosis.
Restore the closing brace for TestColumnarStorageEnabledGateColumnarIndex so CI build and check_dev can parse the DDL test package again.
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/test check-dev2 |
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@wjhuang2016 @bb7133 PTAL again |
Re-check tidb_columnar_storage_enabled in onCreateColumnarIndex at StateNone so ON->OFF between enqueue and owner execution cannot persist a columnar index. Add a vector-index job-side regression test.
Default to the in-memory InfoSchema snapshot and expose reloaded in the response so operators can opt into schema sync without treating can_disable as a lock.
Make the job-arg flag name match its only purpose: bypassing the columnar storage enabled check for placement-rule repair paths.
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/test pull-br-integration-test |
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[LGTM Timeline notifier]Timeline:
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| KeyspaceID: uint32(h.Store.GetCodec().GetKeyspaceID()), | ||
| TiDBColumnarStorageEnabled: variable.BoolToOnOff(variable.TiDBOptOn(enabledVal)), | ||
| ColumnarStoreType: config.GetGlobalConfig().CSE.ColumnarStoreType, | ||
| CanDisable: tableCount == 0, |
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I have a little concern here...we have can_disable = true even when tidb_columnar_storage_enabled = true, what if there's an ongoing adding tiflash replica DDL job here?
Is it better to make can_disable=true when tablecount = 0 & tidb_columnar_storage_enabled=false?
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As described in the issue, the global variable tidb_columnar_storage_enabled should be managed by the operations team (e.g., Tidbcloud). Furthermore, SEMv2 should prevent users from modifying this global variable themselves; only the operations team can modify it.
I believe the specific process should be as follows:
- The "Columnar Storage enable/disable" action is initiated by the user. Before the user performs this action, we should inform them in the documentation and on the Tidbcloud interface that this will cause a loss of TiFlash query capabilities. Users should be prompted to confirm that they truly do not need this feature before disabling it. Users should use operational measures to prevent them from adding TiFlash replicas during this period.
- After the user confirms the click, platforms such as the Tidbcloud control plane should query and confirm the "current schema snapshot" via HTTP API, and based on the
can_disableresponse, best-effort to prevent accidental user actions.
- If
can_disablereturns false, the user is informed that there are still un-cleaned TIFlash replicas and they need to clean them up manually. The control plane does not modify the value oftidb_columnar_storage_enabled. - If
can_disablereturns true, the control plane setstidb_columnar_storage_enabledto false using the SEMv2 mechanism. This ensures at the DDL level that users will not mistakenly add TIFlash replicas later. Then, the control plane performs tasks such as scaling down and taking TIFlash hardware resources offline.
Therefore, the condition can_disable=true should not be subject to the restriction && tidb_columnar_storage_enabled=false.
For ongoing tiflash replica addition operations:
- First, documentation should guide users to determine if they do not need columnar storage functionality, avoiding adding Tiflash replicas during this period;
- The control plane can choose to, after successfully setting
tidb_columnar_storage_enabled=false, confirm via HTTP API whether there are any corner cases in the cluster where the user successfully added a Tiflash replica between steps 2 and 2.2. If so, send a notification to the user informing them of the risk. Users can still remove the Tiflash replica by settingtiflash replica 0or re-enable the functionality through the tidbcloud interface.
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Please open a document PR for this
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: bb7133, wjhuang2016, yudongusa, YuJuncen 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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/cherry-pick release-nextgen-202603 |
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@JaySon-Huang: new pull request created to branch DetailsIn response to this:
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…2603 Keep release createColumnarIndex order and only add the columnar storage gate; drop Kill-cancel test that depends on pingcap#70508; adapt HTTP summary test to the branch startServer API; set handler tests shard_count to 47.
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What problem does this PR solve?
Issue Number: close #70524
Problem Summary:
On TiDB Cloud clusters,
ALTER TABLE/DATABASE ... SET TIFLASH REPLICA n(n > 0) can succeed even when there is no tiflash-compute node is deployed. TiDB persistsTiFlashReplicametadata, but replicas never become ready (or queries time out). The same metadata can also be copied or auto-created byCREATE TABLE LIKE,CREATE TABLEwith a columnar/vector/fulltext index, and leftover-replicaALTER TABLE ADD COLUMNAR INDEX.What changed and how does it work?
Add a cluster-level DDL gate via the global system variable
tidb_columnar_storage_enabled(defaultONfor upgrade compatibility).cse.columnar-store-typeiscolumnarorboth. Classic TiFlash (tiflash) is unchanged.Domain.GetGlobalVar), so the DDL path does not issue a PD RPC. Cache/domain read failure is fail-closed.ON/1(variable.TiDBOptOn) are accepted. Unknown values,OFF, and0are rejected. Rejection errors include the cached value as(tidb_columnar_storage_enabled=%q)for diagnosis.SET TIFLASH REPLICA 0is always allowed so replica cleanup still works.readonly+hidden; onlyRESTRICTED_VARIABLES_ADMIN(control plane) can change it. That restriction lives in control-plane SEM config, not in this repo.Submit-path and job-path both check (same pattern as
checkTiFlashReplicaCount):ALTER TABLE ... SET TIFLASH REPLICA n(n > 0) andALTER DATABASE ... SET TIFLASH REPLICA nALTER DATABASEis aligned with the single-table path: the gate runs only aftershouldModifyTiFlashReplicafinds a table that actually needs a job, so an OFF-cluster no-op (every table already at the target replica count) succeedsCREATE TABLE/CREATE TABLE LIKEwhen the new table would persistTiFlashReplica.Count > 0CREATE TABLEwith a columnar/vector/fulltext index (auto-sets replica count 1); error is remapped toUnsupported add columnar index: Columnar Storage is not enabledALTER TABLE ADD COLUMNAR INDEXeven if a leftover replica already existsInternal placement-rule repair (
refreshTiFlashPlacementRules) submitsActionSetTiFlashReplicawithSetTiFlashReplicaArgs.Internal = trueso the job skips the gate. That path reconstructs missing PD rules for existing replica metadata; it is not a user opt-in to add replicas.Also add status HTTP
GET /tiflash/replicafor a keyspace-scoped live TiFlash replica summary (tidb_columnar_storage_enabled,columnar_store_type,table_count,can_disable). POST is not registered on this path (405).Next-Gen Snapshot BR keep stripping
TiFlashReplicainPreCheckTableTiFlashReplica. The warn log now includestidb_columnar_storage_enabledfrom the BR-embedded Domain sysvar cache (read failure is logged asunavailableand does not block restore). The flag is diagnostic-only and does not change whether Next-Gen strips replicas.Out of scope / known follow-ups:
both+OFF: BRCreateTableWithInfo/BatchCreateTableWithInfo(WithIDAllocated) can still fail when restoring tables that already carry TiFlash replica metadata.Check List
Tests
Manual verification on local tiup cluster
j3(next-gen TiDB,make server NEXT_GEN=1,tiup cluster patch -R tidb):cse.columnar-store-type=columnar: variable ON/OFF;SET TIFLASH REPLICA/CREATE TABLE LIKE/ columnar index gated as expected;SET REPLICA 0allowed; SYSTEM vs ks1 globals do not leak=tiflash: gate skipped while variable remains writable=both: gate still applies (store-count check may run first)SEM v2 (
readonly+hidden): onlyRESTRICTED_VARIABLES_ADMINcan change the variable; DDL gate still enforcedGET /tiflash/replicaon status ports: keyspace-scoped summary (can_disable/table_count/columnar_store_type); POST returns 405No need to test
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Summary by CodeRabbit
New Features
tidb_columnar_storage_enabledsetting, enabled by default.GET /tiflash/replicawith replica counts, storage status, keyspace details, store type, and disable eligibility.Bug Fixes