postgreSQL pgfincore introduces pgfincore 和shared buffer不同，是OS层面的缓存，可以把大对象缓存到OS的cache里，其实就是内存，所以机器的内存配置越大越好，至于oracle是缓存到buffer_pool_keep，可以手工刷出，不过这个是database的缓存，和pg的share
postgreSQL pgfincore introduces
pgfincore 和shared buffer不同，是OS层面的缓存，可以把大对象缓存到OS的cache里，其实就是内存，所以机器的内存配置越大越好，至于oracle是缓存到buffer_pool_keep，可以手工刷出，不过这个是database的缓存，和pg的shared buffer同理。这里就不再详细介绍。
1.下载wget http://pgfoundry.org/frs/download.php/3186/pgfincore-v1.1.1.tar.gz
2.解压下载的安装包tar -zxvf pgfincore-v1.1.1.tar.gz
3.复制解压后的目录到pg源代码目录/contrib
4.安装：
postgres用户：
make clean
make
su - root
source /home/postgres/.bash_profile
make install
根据READ.rst
For PostgreSQL >= 9.1, log in your database and::
mydb=# CREATE EXTENSION pgfincore;
For other release, create the functions from the sql script (it should be in
your contrib directory)::
psql mydb -f pgfincore.sql
postgres=# select version();
version
---------------------------------------------------
PostgreSQL 9.1.2 on x86_-unknown-linux-gnu, compiled by gcc (GCC) 4.1.2 20071124 (Red Hat 4.1.2-42), -bit
postgres=# CREATE EXTENSION pgfincore;
CREATE EXTENSION
postgres=# select * from pg_extension ;
extname | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition
----------------+----------+--------------+----------------+------------+-----------+--------------
plpgsql | 10 | 11 | f | 1.0 | |
pg_buffercache | 10 | 2200 | t | 1.0 | |
pgfincore | 10 | 2200 | t | 1.1.1 | |
pgfincore使用：
pgfincore 对象的cache情况
pgfadvise_willneed 将对象刷入cache
pgfadvise_dontneed 将对象刷出cache
pgfadvise_loader 直接和page cache交互，加载，卸载页面
pgsysconf 操作系统的cache情况
pgsysconf_pretty同上，只不过输更易懂，带上了单位。
postgres=# \d t
Table "public.t"
Column | Type | Modifiers
--------+---------+-----------------------------------------------
s | integer | not null default nextval('t_s_seq'::regclass)
i | integer |
postgres=# insert into t(i) values (generate_series(1,10000000));
INSERT 0 10000000
postgres=# select pg_size_pretty(pg_relation_size('t'));
pg_size_pretty
----------------
346 MB
当前文件系统的使用情况：pgsysconf()，pgsysconf_pretty()
postgres=# select * from pgsysconf();
os_page_size | os_pages_free | os_total_pages
--------------+---------------+----------------
4096 | 182787 | 2044328
postgres=# select * from pgsysconf_pretty();
os_page_size | os_pages_free | os_total_pages
--------------+---------------+----------------
4096 bytes | 721 MB | 7986 MB
(1 row)
表t的使用情况：pgfincore
postgres=# select * from pgfincore('t');
relpath | segment | os_page_size | rel_os_pages | pages_mem | group_mem | os_pages_free | databit
------------------+---------+--------------+--------------+-----------+-----------+---------------+---------
base/12699/141 | 0 | 4096 | 88496 | 88496 | 1 | 181767 |
os_page_size：文件系统页大小
rel_os_pages：占用文件系统页数量
pages_mem：有多少文件系统页在系统cache
刷入cache：pgfadvise_willneed()
postgres=# select * from pgfadvise_willneed('t');
relpath | os_page_size | rel_os_pages | os_pages_free
------------------+--------------+--------------+---------------
base/12699/141 | 4096 | 88496 | 1828
(1 row)
postgres=# select * from pgfincore('t');
relpath | segment | os_page_size | rel_os_pages | pages_mem | group_mem | os_pages_free | databit
------------------+---------+--------------+--------------+-----------+-----------+---------------+---------
base/12699/141 | 0 | 4096 | 88496 | 88496 | 1 | 186397 |
(1 row)
刷出cache：
postgres=# select * from pgfadvise_dontneed('t');
relpath | os_page_size | rel_os_pages | os_pages_free
------------------+--------------+--------------+---------------
base/12699/141 | 4096 | 88496 | 275021
(1 row)
postgres=# select * from pgfincore('t');
relpath | segment | os_page_size | rel_os_pages | pages_mem | group_mem | os_pages_free | databit
------------------+---------+--------------+--------------+-----------+-----------+---------------+---------
base/12699/141 | 0 | 4096 | 88496 | 0 | 0 | 275052 |
(1 row)
pgfadvise_loader:
postgres=# select * from pgfadvise_loader('t', 0, true, true, B'111000');
relpath | os_page_size | os_pages_free | pages_loaded | pages_unloaded
------------------+--------------+---------------+--------------+----------------
base/12699/141 | 4096 | 186626 | 3 | 3
(1 row)
loading：
postgres=# select * from pgfadvise_loader('t', 0, true, false, B'111000');
relpath | os_page_size | os_pages_free | pages_loaded | pages_unloaded
------------------+--------------+---------------+--------------+----------------
base/12699/141 | 4096 | 1860 | 3 | 0
(1 row)
unloading：
postgres=# select * from pgfadvise_loader('t', 0, false, true, B'111000');
relpath | os_page_size | os_pages_free | pages_loaded | pages_unloaded
------------------+--------------+---------------+--------------+----------------
base/12699/141 | 4096 | 186557 | 0 | 3
(1 row)
pgfadvise_NORMAL
pgfadvise_SEQUENTIAL
pgfadvise_RANDOM
这几个可以指定当前内存的属性，正常，顺序，还是随机。
快照与恢复：
做快照：
create table pgfincore_snapshot as
select 't'::text as relname,*,now() as date_snapshot
from pgfincore('t',true);
应用快照：
select * from pgfadvise_loader('t', 0, true, true,
(select databit from pgfincore_snapshot
where relname='t' and segment = 0));
relpath | os_page_size | os_pages_free | pages_loaded | pages_unloaded
------------------+--------------+---------------+--------------+----------------
base/12699/141 | 4096 | 186259 | 88490 | 6
(1 row)
postgres=# select * from pgfincore('t');
relpath | segment | os_page_size | rel_os_pages | pages_mem | group_mem | os_pages_free | databit
------------------+---------+--------------+--------------+-----------+-----------+---------------+---------
base/12699/141 | 0 | 4096 | 88496 | 88490 | 2 | 186097 |
(1 row)
可以看到 88496 和88490，有几个页面是刷出cache，所以不相等
select * from pgfadvise_willneed('t');
postgres=# select * from pgfincore('t');
relpath | segment | os_page_size | rel_os_pages | pages_mem | group_mem | os_pages_free | databit
------------------+---------+--------------+--------------+-----------+-----------+---------------+---------
base/12699/141 | 0 | 4096 | 88496 | 88496 | 1 | 186227 |
(1 row)
：
*PgFincore needs mincore() and POSIX_FADVISE.
*PgFincore has a limited mode when POSIX_FADVISE is not provided by the platform.
*PgFincore needs PostgreSQL >= 8.3
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