checksum might mismatch with parallel import if some instances runs too fast

[D3Hunter]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

if some instance finished import right before we do checksum, the already imported data will be calculated twice, and cause checksum mismatch

tidb/lightning/pkg/importer/meta_manager.go

Lines 330 to 332 in 851af35

	if (newRowIDBase > 0 || !needAutoID) && m.needChecksum && baseTotalKvs == 0 {
	remoteCk, err := DoChecksum(ctx, m.tr.tableInfo)
	if err != nil {

it's very hard to reproduce this, it requires

• current instance should be very slow
• another instance runs very fast, and the data should be quite small

so just record this and mark as minor

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)