currently we have a very basic implementation of the SortOperator and a very basic rule for cross-server sorting plan generator. It generates an sort exchange which connects a local sorting prior to exchange then follow by a remote sorting on a single machine
this is originally designed for large quantity sorting and streaming responses. but none of those were implemented in SortOperator

Improvement

1. for the current SortOperator implementation, the sort-exchange can be simplified to a normal exchange, and the local sort prior to exchange can be removed.
   • [multistage][bugfix] improve sort copy rule #12237
   • [multistage][bugfix] relax sort copy rule to always push limit if no collation #12251
2. for longer term we should support 2 strategies:
   • when data size is small, we should follow the 1st approach;
   • when data size is large, we should
     (a) create a local sort before the exchange, (either via sort-exchange, or via additional sort operator);
     (b) do a k-merge sort on the single-machine global sorting operator
     (c) stream the results back (which is possible with k-merge)