Users need to look at a few random pieces of data in a table to see what the data looks like. So users often use the SQL:
"select * from table limit 10"
For a large table, expect to end soon because only a few pieces of data are queried.
For DataStream or BoundedStream, they are push based execution models, so the downstream cannot control the end of source operator.
We need push down limit to source operator, so that source operator can end early.