Test TestExchangePartitionWithPlacement fails after injecting full reload

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Enable info schema cache V2.

Modify codes

func (do *Domain) tryLoadSchemaDiffs(m *meta.Meta, usedVersion, newVersion int64, startTS uint64) (infoschema.InfoSchema, *transaction.RelatedSchemaChange, []string, error) {
	var diffs []*model.SchemaDiff
	for usedVersion < newVersion {
		usedVersion++
		diff, err := m.GetSchemaDiff(usedVersion)
		if err != nil {
			return nil, nil, nil, err
		}
		if diff == nil {
			// Empty diff means the txn of generating schema version is committed, but the txn of `runDDLJob` is not or fail.
			// It is safe to skip the empty diff because the infoschema is new enough and consistent.
			logutil.BgLogger().Info("diff load InfoSchema get empty schema diff", zap.Int64("version", usedVersion))
			do.infoCache.InsertEmptySchemaVersion(usedVersion)
			continue
		}
		diffs = append(diffs, diff)
	}
	if diffs[0].Type == model.ActionExchangeTablePartition {
		return nil, nil, nil, errors.New("mock error")
	}
	builder, err := infoschema.NewBuilderV3(do, do.sysFacHack, do.infoCache.Data).InitWithOldInfoSchema(do.infoCache.GetLatest())
	if err != nil {
		return nil, nil, nil, errors.Trace(err)
	}

Inject mock error if DDL type is ActionExchangeTablePartition.

2. What did you expect to see? (Required)

Test TestExchangePartitionWithPlacement passes.

3. What did you see instead (Required)

Test TestExchangePartitionWithPlacement fails.

4. What is your TiDB version? (Required)

master

[wjhuang2016]

Root cause analysis:

infoData calls remove() only in applyDropTableV2.
If the schema is fully reloaded instead of partially reloaded, the table that should be removed from the B-tree cache is still there. Then the later used would be incorrect.