go-mydumper some problems

[Dragonzlx]

Hi, i am using go-mydumper in mysql 8.0.19 group replication， it failed to restore a table with 70M, i check the mysql error log, it seems too much memory when go-mydumper to restore, so it lead to mysql out of memory, and lead to node kick out from the cluster, there is some suggestion on below:

1. myloader consumes too much memory to restore from a backup
2. it should be better to add parallel options to backup

[BohuTANG]

1. Need to determine who use the the memory first, go-mydumper is streaming fetch, it's memory efficent.
2. go-mydumper is parallel based on database