oracle consistent gets,consistent gets很高，怎样调整？

select dept_no, count(m2d.m_2_d_id) as all_count

from a_m_plan_day    m2d,

a_m_plan_series series,

a_m_plan_class  planClass,

a_m_plan_prj    prj

where m2d.m_plan_prj_id = prj.m_plan_prj_id and

prj.m_plan_class_id = planClass.m_plan_class_id and

planClass.m_series_id = series.m_series_id and

series.month_period = substr('20071100', 0, 6) and

dept_no in ('00242102')

group by dept_no

SQL> /

DEPT_NO

--------------------------------------------------------------------------------

ALL_COUNT

----------

00242102

1407

Execution Plan

----------------------------------------------------------

0      SELECT STATEMENT Optimizer=CHOOSE (Cost=28 Card=17 Bytes=113

9)

1    0   SORT (GROUP BY NOSORT) (Cost=28 Card=17 Bytes=1139)

2    1     NESTED LOOPS (Cost=28 Card=17 Bytes=1139)

3    2       MERGE JOIN (CARTESIAN) (Cost=28 Card=108888 Bytes=6424

392)

4    3         NESTED LOOPS (Cost=5 Card=1 Bytes=55)

5    4           TABLE ACCESS (FULL) OF 'A_M_PLAN_SERIES' (Cost=4 C

ard=1 Bytes=48)

6    4           INDEX (RANGE SCAN) OF 'IDX_M_PLAN_CLASS' (UNIQUE)

(Cost=1 Card=6470 Bytes=45290)

7    3         BUFFER (SORT) (Cost=27 Card=9 Bytes=36)

8    7           INDEX (FAST FULL SCAN) OF 'IDX_M_PLAN_DAY' (NON-UN

IQUE) (Cost=23 Card=9 Bytes=36)

9    2       INDEX (UNIQUE SCAN) OF 'IDX_M_PLAN_PRJ' (UNIQUE)

Statistics

----------------------------------------------------------

0  recursive calls

2  db block gets

10389847  consistent gets

15429  physical reads

0  redo size

562  bytes sent via SQL*Net to client

655  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

1  sorts (disk)

1  rows processed

SQL> /