Oracle

• check stats enabled:

SELECT DBMS_STATS.get_prefs('PUBLISH') FROM dual;

• list of tables ordered by size

select segment_name,segment_type,bytes ,max_size  from user_segments  ORDER BY bytes DESC

• disable constraint

alter table table_name  disable constraint <constraint>;

• enable constraint

alter table table_name  enable constraint <constraint>;

• empty table and release space

truncate table table_name DROP STORAGE;