How to evaluate "explain analyze" correctly soon after "explain" for the same statement ?

Hi all:

I have one question about the cache clearing.

If I use the following soon after database startup(or first time I use it):

postgres=# explain analyze select id,deptno from gaotab where id=200;

QUERY
PLAN

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

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

Index Only Scan using idx_id_dept on gaotab (cost=0.00..8.27 rows=1
width=8) (

actual time=30.912..30.915 rows=1 loops=1)

Index Cond: (id = 200)

Heap Fetches: 1

Total runtime: 47.390 ms

(4 rows)

postgres=#

The result is: the above explain analyze got a total runtime of 47 ms.

But If I restart the database again, and then execute the following:

postgres=# explain select id,deptno from gaotab where id=200;

QUERY
PLAN

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

Index Only Scan using idx_id_dept on gaotab (cost=0.00..8.27 rows=1
width=8)

Index Cond: (id = 200)

(2 rows)

postgres=# explain analyze select id,deptno from gaotab where id=200;

QUERY
PLAN

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

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

Index Only Scan using idx_id_dept on gaotab (cost=0.00..8.27 rows=1
width=8) (

actual time=0.052..0.053 rows=1 loops=1)

Index Cond: (id = 200)

Heap Fetches: 1

Total runtime: 0.074 ms

(4 rows)

This time I got the total runtime of 0.074ms, obviously the explain
analyze benefit from the explain statement.

It might not be a big problem in a small system.

But when in a production environment, When I want to use explain and
then , soon use explain analyze for the same statement,

How can I avoid the influence of cache and get the right answer for
evaluating purpose?

It is not a good idea to restart the database again and again I think.

I wonder is there any method of clearing cache or even clear only a
particular part of the cache?

In my test environment, I can get the following:

postgres=# show seq_page_cost;

seq_page_cost

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

1

(1 row)

postgres=# show cpu_tuple_cost;

cpu_tuple_cost

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

0.01

(1 row)

postgres=# show cpu_operator_cost;

cpu_operator_cost

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

0.0025

(1 row)

And my table is like that：

postgres=# analyze;
ANALYZE
postgres=# select a.relpages, a.reltuples,
a.relfilenode,a.reltype,b.typname from pg_class a, pg_type b where
a.relname like 'gaotab%' and a.reltype=b.oid;
relpages | reltuples | relfilenode | reltype | typname
----------+-----------+-------------+---------+---------
7 | 1000 | 16396 | 16386 | gaotab
(1 row)

Thanks in advance.