Создадим БД и таблицу
~~~~~~~~~~~~~~~~~~~~~


=> create database db7;
CREATE DATABASE

=> \c db7
You are now connected to database "db7" as user "postgres".

=> create table t(n numeric);
CREATE TABLE

=> insert into t select 1 from generate_series(1,10000);
INSERT 0 10000

Сколько страниц на диске у t?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


=> select pg_total_relation_size('t')/8192;
 ?column? 
----------
       49
(1 row)


Сколько буферов в кэше для t?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


=> create extension pg_buffercache;
CREATE EXTENSION

=> select count(*)
=> from   pg_buffercache b,
=>        pg_class c
=> where  b.reldatabase = (select oid from pg_database where datname = current_database())
=> and    c.oid = 't'::regclass
=> and    b.relfilenode = c.relfilenode;
 count 
-------
    47
(1 row)


Сколько грязных буферов в кэше?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


=> select count(*)
=> from   pg_buffercache b
=> where  isdirty;
 count 
-------
    95
(1 row)


Контрольная точка
~~~~~~~~~~~~~~~~~


=> checkpoint;
CHECKPOINT

=> select count(*)
=> from   pg_buffercache b
=> where  isdirty;
 count 
-------
     0
(1 row)


(Грязных буферов не осталось.)

=> \q