splitFactor阈值设定

源码当中，这个阈值是Job维度的，一个Job下可能有多个conns，有的conn下表数据量大，有的小，阈值怎么设定？支持数据源级别的阈值配置吗？

The issue identifies only the Job-level splitFactor threshold and does not name a file, test, or entry point. Start by locating where splitFactor is configured and applied across Jobs and connections, then determine whether datasource-level configuration is supported. Done requires an agreed configuration behavior that handles connections with different table sizes.

Written by the indexing model from the issue text.