Queries on DBA_FREE_SPACE are Slow

One of our production database appeared that tablespaces size monitoring scirpt was very slow, we are using dba_free_space view in our script, Database version is 12.2.0.1.0.
For solving problem I started with gathering statistics:

begin
  dbms_stats.gather_system_stats();

end;
/
begin
  dbms_stats.gather_fixed_objects_stats();
  
end;
/
begin
  dbms_stats.gather_dictionary_stats();
  
end;

After that  queries on dba_free_space was little bit faster, but still slow.
Than I tried to view really what was behind dba_free_space and found that it also queries recyclebin and if in your recyclebin is many objects than it will be cause of slow queries on dba_free_space :

select TEXT from dba_views where view_name='DBA_FREE_SPACE';

select ts.name, fi.file#, f.block#,
       f.length * ts.blocksize, f.length, f.file#
from sys.ts$ ts, sys.fet$ f, sys.file$ fi
where ts.ts# = f.ts#
  and f.ts# = fi.ts#
  and f.file# = fi.relfile#
  and ts.bitmapped = 0
union all
select
       ts.name, fi.file#, f.ktfbfebno,
       f.ktfbfeblks * ts.blocksize, f.ktfbfeblks, f.ktfbfefno
from sys.ts$ ts, sys.x$ktfbfe f, sys.file$ fi
where ts.ts# = f.ktfbfetsn
  and f.ktfbfetsn = fi.ts#
  and f.ktfbfefno = fi.relfile#
  and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0
  and bitand(ts.flags, 4503599627370496) <> 4503599627370496
union all
select
       ts.name, fi.file#, u.ktfbuebno,
       u.ktfbueblks * ts.blocksize, u.ktfbueblks, u.ktfbuefno
from sys.recyclebin$ rb, sys.ts$ ts, sys.x$ktfbue u, sys.file$ fi
where ts.ts# = rb.ts#
  and rb.ts# = fi.ts#
  and u.ktfbuefno = fi.relfile#
  and u.ktfbuesegtsn = rb.ts#
  and u.ktfbuesegfno = rb.file#
  and u.ktfbuesegbno = rb.block#
  and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0
  and bitand(ts.flags, 4503599627370496) <> 4503599627370496
union all
select ts.name, fi.file#, u.block#,
       u.length * ts.blocksize, u.length, u.file#
from sys.ts$ ts, sys.uet$ u, sys.file$ fi, sys.recyclebin$ rb
where ts.ts# = u.ts#
  and u.ts# = fi.ts#
  and u.segfile# = fi.relfile#
  and u.ts# = rb.ts#
  and u.segfile# = rb.file#
  and u.segblock# = rb.block#
  and ts.bitmapped = 0
union all
select
       ts.name, fi.file#, f.extent_start,
       (f.extent_length_blocks_2K /(ts.blocksize/2048)) * ts.blocksize,
       (f.extent_length_blocks_2K / (ts.blocksize/2048)), fi.relfile#
from sys.ts$ ts, sys.new_lost_write_extents$ f, sys.file$ fi
where ts.ts# = f.extent_datafile_tsid
  and f.extent_datafile_tsid = fi.ts#
  and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0
  and bitand(ts.flags, 4503599627370496) = 4503599627370496

Solution: just purge dba_recyclebin and queries will fly on dba_free_space

purge dba_recyclebin;