ddl: ddl rollingback error may lead the json unmarshal error(2)

[AilinKid]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Take cancel add index for example, let mock the error code in Line 45 of rollingback.go with hash e1fccc6

func convertAddIdxJob2RollbackJob(t *meta.Meta, job *model.Job, tblInfo *model.TableInfo, indexInfo *model.IndexInfo, err error) (int64, error) {
	job.State = model.JobStateRollingback
        // here
	return 0, errors.New("mock update version and tableInfo error")
	if indexInfo.Primary {
		nullCols, err := getNullColInfos(tblInfo, indexInfo)
		if err != nil {
			return 0, errors.Trace(err)
		}
		for _, col := range nullCols {
			// Field PreventNullInsertFlag flag reset.
			col.Flag &^= mysql.PreventNullInsertFlag
		}
	}

For the sake of manual cancel operation, let hang on StateDeleteOnly in Line507 with index.go for a while in which we can execute admin cancel ddl job jobID in the other client.

	case model.StateDeleteOnly:
		time.Sleep(time.Second * 20)
		// delete only -> write only
		indexInfo.State = model.StateWriteOnly

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

Since convertAddIdxJob2RollbackJob encounters an error in the internal logic, we should keep the job state as it is (canceling) and record the error count and message wait for the next ddl round. Once the error count is beyond the limitation, it job is canceled directly.

3. What did you see instead (Required)

Since convertAddIdxJob2RollbackJob encounters an error in the internal logic, the job can't be set as JobStateRollingback at every first beginning. That will leads to the rollbacking logic done with something like ERROR 1105 (HY000): json: cannot unmarshal bool into Go value of type string

4. What is your TiDB version? (Required)

master

[ti-srebot]

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