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*: fix a bug that update statement uses point get and update plan with different tblInfo (#54183) #54257

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@ti-chi-bot ti-chi-bot commented Jun 27, 2024

This is an automated cherry-pick of #54183

What problem does this PR solve?

Issue Number: close #53634

Problem Summary:

Case

Init SQLs:

CREATE TABLE stock ( a int NOT NULL, b char(30) NOT NULL,  c int, d char(64), PRIMARY KEY(a,b)) ;
insert into stock values(1, 'a', 11, 'x'), (2, 'b', 22, 'y');
alter table stock add column cct_1 int default 10;
alter table stock modify cct_1 json;
alter table stock add column adc_1 smallint;
  • Step1. using conn1
    prepare statements:
    begin;
    SELECT a, c, d from stock where (a, b) IN ((?, ?),(?, ?)) FOR UPDATE;
    UPDATE stock SET c = ? WHERE a= ? AND b = 'a';
    UPDATE stock SET c = ?, d = 'z' WHERE a= ? AND b = 'b';
    commit;

run a statement:
begin;

  • Step2. using conn2
    do DDL:
    alter table stock drop column cct_1;
  • Step3. using conn1
    When the DDL is in Write-Only state
    exec statements:
    SELECT a, c, d from stock where (a, b) IN ((?, ?),(?, ?)) FOR UPDATE;
    UPDATE stock SET c = ? WHERE a= ? AND b = 'a';
    UPDATE stock SET c = ?, d = 'z' WHERE a= ? AND b = 'b';
    commit;
  • Step4. using conn1
    Check the result
    select * from stock;

  • Statement execution order table

conn1 conn2
step1. prepare stmts
step1. begin;
step2. alter table stock drop column cct_1; (state public -> write-only)
step3. exec stmts write-only
step2. alter table stock drop column cct_1; (finish)
step4. select * from stock;

Conclusion

The update statement in step3 uses point get and update plan, but the tblInfo used by the two plans is inconsistent, resulting in incorrect data in real storage.

  • After executing step3. select statement, the stock is locked in GetRelatedTableForMDL, so stmt.tbls[i].Meta().Revision != newTbl.Meta().Revision is false. It means schemaNotMatch is false. So we needn't to Preprocess.

    newTbl, err := tryLockMDLAndUpdateSchemaIfNecessary(sctx.GetPlanCtx(), stmt.dbName[i], stmt.tbls[i], is)
    if err != nil {
    schemaNotMatch = true
    continue
    }
    if stmt.tbls[i].Meta().Revision != newTbl.Meta().Revision {

  • Step3. update statement using tblName.TableInfo(get it when preparing statements, cct_1 is public) in newPointGetPlan.

    tbl := tblName.TableInfo

  • Step3. update statement using t gets from is.TableByID(tbl.ID)( cct_1 is write-only)

    updatePlan.names = pointPlan.OutputNames()
    is := ctx.GetInfoSchema().(infoschema.InfoSchema)
    t, _ := is.TableByID(tbl.ID)
    updatePlan.tblID2Table = map[int64]table.Table{
    tbl.ID: t,
    }

What changed and how does it work?

Add the Revision field comparison of tbl(get from txn infoschema) and newTbl to confirm whether reprocess is required.

Check List

Tests

  • Unit test
  • Integration test
  • Manual test (add detailed scripts or steps below)
  • No need to test
    • I checked and no code files have been changed.

Side effects

  • Performance regression: Consumes more CPU
  • Performance regression: Consumes more Memory
  • Breaking backward compatibility

Documentation

  • Affects user behaviors
  • Contains syntax changes
  • Contains variable changes
  • Contains experimental features
  • Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Fix an issue where improper use of metadata locks in some scenarios could cause abnormal data to be written when using the plan cache.

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ti-chi-bot bot commented Jun 27, 2024

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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ti-chi-bot bot commented Jun 27, 2024

[APPROVALNOTIFIER] This PR is NOT APPROVED

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@ti-chi-bot ti-chi-bot bot added size/XL Denotes a PR that changes 500-999 lines, ignoring generated files. and removed size/L Denotes a PR that changes 100-499 lines, ignoring generated files. labels Jun 27, 2024
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ti-chi-bot bot commented Jun 27, 2024

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name Commit Details Required Rerun command
idc-jenkins-ci-tidb/build e5c435d link true /test build
idc-jenkins-ci-tidb/unit-test e5c435d link true /test unit-test
idc-jenkins-ci-tidb/check_dev e5c435d link true /test check-dev
idc-jenkins-ci-tidb/check_dev_2 e5c435d link true /test check-dev2

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