## Proposed changes
When a delete error occurs, the error message is ambiguous.
```sql
mysql> DELETE FROM nebula_trade_health_trade PARTITION q3_2021 WHERE event_day = '20210706';
ERROR 1064 (HY000): errCode = 2, detailMessage = failed to execute delete. transaction id 7215554, timeout(ms) 160000, unfinished replicas: 4718319=7345841
```
We do not know the meaning of `4718319=7345841`.
Actually the former is `BackendId` and the latter is `TabletId`.
I'll add an instruction here to help locate the problem quickly. The error message will be
```sql
ERROR 1064 (HY000): errCode = 2, detailMessage = failed to execute delete. transaction id 7215554, timeout(ms) 160000, unfinished replicas [BackendId=TabletId]: 4718319=7345841
```
3ad12c5f8a