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‎201103/20110329_01.md‎

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‎201103/readme.md‎

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### 文章列表
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----
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##### 20110329_01.md [《TOAST,The Oversized-Attribute Storage Technique》](20110329_01.md)

‎201201/20120105_01.md‎

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## TOAST table with pgfincore
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### 作者
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digoal
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### 日期
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2012-01-05
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### 标签
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PostgreSQL , toast , 内存持久化 , pg_fadvise , flag , pgfincore
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----
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## 背景
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pgfincore 可以修改文件的posix_advise属性，输入参数是对象名。如表名，索引名。
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注意有些PostgreSQL数据类型的存储如果选择了为extended或者EXTERNAL存储时。实际上这些内容是存储在TOAST表里面。
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例如text 类型.
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下面来看一个例子 :
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```
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digoal=> \d text
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Table "digoal.text"
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Column | Type | Modifiers
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--------+---------+-----------
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id | integer | not null
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info | text |
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Indexes:
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"text_pkey" PRIMARY KEY, btree (id), tablespace "digoal_idx"
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```
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这个表有个toast表, 如下 :
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```
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digoal=> select relname from pg_class where oid=(select reltoastrelid from pg_class where relname='text');
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relname
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------------------
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pg_toast_1293339
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```
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还有个toast索引 :
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```
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digoal=> select relname from pg_class where oid=(select reltoastidxid from pg_class where oid=(select reltoastrelid from pg_class where relname='text'));
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relname
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------------------------
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pg_toast_1293339_index
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```
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下面我想把text表的posix_fadvise修改一下 :
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```
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digoal=> select * from pgfadvise_willneed('text');
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relpath | os_page_size | rel_os_pages | os_pages_free
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------------------------------------------------+--------------+--------------+---------------
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pg_tblspc/16392/PG_9.1_201105231/16394/6124614 | 4096 | 64922 | 30319
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digoal=> select * from pgfadvise_willneed('text_pkey');
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relpath | os_page_size | rel_os_pages | os_pages_free
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------------------------------------------------+--------------+--------------+---------------
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pg_tblspc/16393/PG_9.1_201105231/16394/6124616 | 4096 | 27424 | 31007
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```
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显然没有包含TOAST表的内容。
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接下来看看如何包含TOAST表的内容 :
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首先要看看TOAST表放在哪个schema下面 :
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```
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digoal=> select nspname from pg_namespace where oid=(select relnamespace from pg_class where oid=1293342);
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nspname
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----------
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pg_toast
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```
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pg_toast的owner是postgres, 因此需要使用超级用户 :
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```
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digoal=> \dn *.*
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List of schemas
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Name | Owner
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--------------------+----------
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digoal | digoal
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information_schema | postgres
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pg_catalog | postgres
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pg_temp_1 | postgres
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pg_toast | postgres
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pg_toast_temp_1 | postgres
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public | postgres
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```
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接下来就可以把TOAST表和它的索引放入内存了 :
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```
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digoal=# select * from pgfadvise_willneed('pg_toast.pg_toast_1293339');
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relpath | os_page_size | rel_os_pages | os_pages_free
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---------------------------------------------------+--------------+--------------+---------------
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615 | 4096 | 262144 | 32027
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.1 | 4096 | 262144 | 30055
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.2 | 4096 | 262144 | 31436
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.3 | 4096 | 262144 | 30018
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.4 | 4096 | 262144 | 31654
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.5 | 4096 | 262144 | 29949
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.6 | 4096 | 262144 | 30010
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.7 | 4096 | 262144 | 31135
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.8 | 4096 | 262144 | 30281
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.9 | 4096 | 262144 | 31313
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.10 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.11 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.12 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.13 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.14 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.15 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.16 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.17 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.18 | 4096 | 262144 | 31253
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pg_tblspc/16392/PG_9.1_201105231/16394/6124615.19 | 4096 | 19264 | 31253
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(20 rows)
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digoal=# select * from pgfadvise_willneed('pg_toast.pg_toast_1293339_index');
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relpath | os_page_size | rel_os_pages | os_pages_free
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------------------------------------------------+--------------+--------------+---------------
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pg_tblspc/16392/PG_9.1_201105231/16394/6124617 | 4096 | 54842 | 30332
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(1 row)
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```
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[Count](http://info.flagcounter.com/h9V1)
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‎201201/readme.md‎

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### 文章列表
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----
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##### 20120105_01.md [《TOAST table with pgfincore》](20120105_01.md)

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