Re: CALCITE-4833 review request.

[stanilovsky evgeny]

fixed: gc pressure part still need to additional time, revert this part,  
all other waiting for review.

Guys i found that some kinds of nested subqueries are failed [1].
i.e. SELECT t1.empid FROM emps t1 LEFT JOIN emps t2 ON (SELECT  
t2.empid)<=100
Fix a little bit hack as for me, but all tests are done.
Additionally i fix some redundant gc pressure a bit.
Plz make a review.
thanks !

[1] https://issues.apache.org/jira/browse/CALCITE-4833