migration tool performance optimization

[xiangyu5632]

1. Currently, the data migration tool uses a single thread for data processing. It is hoped to change to multi-threaded concurrency, and at the same time, the problem of data disorder needs to be considered.
2. During the data migration process, the memory is dynamically applied. Due to the frequent application and release of memory, the GC is too frequent, which affects the efficiency of the tool. It is hoped that a certain size of memory space can be applied for at the beginning, and then the memory can be continuously reused to reduce GC. frequency, improve efficiency