postgreSQLpgfincoreintroduces

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_64-unknown-linux-gnu, compiled by gcc (GCC) 4.1.2 20071124 (Red Hat 4.1.2-42), 64-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/12699/16441 | 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/12699/16441 | 4096 | 88496 | 186428

(1 row)

postgres=# select * from pgfincore('t');

relpath | segment | os_page_size | rel_os_pages | pages_mem | group_mem | os_pages_free | databit

------------------+---------+--------------+--------------+-----------+-----------+---------------+---------

base/12699/16441 | 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/12699/16441 | 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/12699/16441 | 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/12699/16441 | 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/12699/16441 | 4096 | 186460 | 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/12699/16441 | 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/12699/16441 | 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/12699/16441 | 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/12699/16441 | 0 | 4096 | 88496 | 88496 | 1 | 186227 |

(1 row)

限制：

*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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