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‎201903/20190331_03.md‎

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## PostgreSQL 12 preview - 意义重大改进：增加一层access manager API - 支持 TABLE、INDEX AM(access method) - 为storage pluggable 开路
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### 作者
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digoal
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### 日期
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2019-03-31
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### 标签
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PostgreSQL , am , indexam , tableam , access method , access manager
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----
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## 背景
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PostgreSQL 12 新增一层 access manager API - 支持 TABLE、INDEX AM(access method) - 为storage pluggable 开路 。
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意义重大：将来支持zheap(undo引擎)，列存储，内存表，压缩表等会非常的便捷。
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PG 11
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![pic](20190331_03_pic_001.jpg)
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PG 12
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![pic](20190331_03_pic_002.jpg)
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[Pluggable Storage in PostgreSQL](20190331_03_pdf_001.pdf)
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```
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CREATE TABLE …(...) USING heap;
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```
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https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=8586bf7ed8889f39a59dd99b292014b73be85342
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```
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tableam: introduce table AM infrastructure.
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This introduces the concept of table access methods, i.e.
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CREATE ACCESS METHOD ... TYPE TABLE and
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CREATE TABLE ... USING (storage-engine).
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No table access functionality is delegated to table AMs as of this
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commit, that'll be done in following commits.
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Subsequent commits will incrementally abstract table access
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functionality to be routed through table access methods. That change
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is too large to be reviewed & committed at once, so it'll be done
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incrementally.
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Docs will be updated at the end, as adding them incrementally would
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likely make them less coherent, and definitely is a lot more work,
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without a lot of benefit.
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Table access methods are specified similar to index access methods,
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i.e. pg_am.amhandler returns, as INTERNAL, a pointer to a struct with
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callbacks. In contrast to index AMs that struct needs to live as long
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as a backend, typically that's achieved by just returning a pointer to
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a constant struct.
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Psql's \d+ now displays a table's access method. That can be disabled
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with HIDE_TABLEAM=true, which is mainly useful so regression tests can
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be run against different AMs. It's quite possible that this behaviour
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still needs to be fine tuned.
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For now it's not allowed to set a table AM for a partitioned table, as
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we've not resolved how partitions would inherit that. Disallowing
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allows us to introduce, if we decide that's the way forward, such a
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behaviour without a compatibility break.
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Catversion bumped, to add the heap table AM and references to it.
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Author: Haribabu Kommi, Andres Freund, Alvaro Herrera, Dimitri Golgov and others
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Discussion:
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https://postgr.es/m/[email protected]
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https://postgr.es/m/[email protected]
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https://postgr.es/m/[email protected]
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https://postgr.es/m/[email protected]
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```
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## 查看当前支持的AM
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```
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postgres=# select * from pg_am;
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oid | amname | amhandler | amtype
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------+--------+----------------------+--------
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2 | heap | heap_tableam_handler | t
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403 | btree | bthandler | i
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405 | hash | hashhandler | i
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783 | gist | gisthandler | i
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2742 | gin | ginhandler | i
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4000 | spgist | spghandler | i
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3580 | brin | brinhandler | i
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(7 rows)
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postgres=# \d+ pg_am
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Table "pg_catalog.pg_am"
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Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
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-----------+---------+-----------+----------+---------+---------+--------------+-------------
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oid | oid | | not null | | plain | |
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amname | name | | not null | | plain | |
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amhandler | regproc | | not null | | plain | |
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amtype | "char" | | not null | | plain | |
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Indexes:
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"pg_am_name_index" UNIQUE, btree (amname)
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"pg_am_oid_index" UNIQUE, btree (oid)
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Access method: heap
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```
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## 扩展AM例子（扩展bloom indexam）
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```
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postgres=# create extension bloom ;
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CREATE EXTENSION
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postgres=# select * from pg_am;
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oid | amname | amhandler | amtype
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-------+--------+----------------------+--------
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2 | heap | heap_tableam_handler | t
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403 | btree | bthandler | i
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405 | hash | hashhandler | i
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783 | gist | gisthandler | i
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2742 | gin | ginhandler | i
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4000 | spgist | spghandler | i
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3580 | brin | brinhandler | i
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23030 | bloom | blhandler | i
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(8 rows)
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postgres=# \dA+
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List of access methods
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Name | Type | Handler | Description
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--------+-------+----------------------+----------------------------------------
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bloom | Index | blhandler | bloom index access method
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brin | Index | brinhandler | block range index (BRIN) access method
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btree | Index | bthandler | b-tree index access method
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gin | Index | ginhandler | GIN index access method
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gist | Index | gisthandler | GiST index access method
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hash | Index | hashhandler | hash index access method
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heap | Table | heap_tableam_handler | heap table access method
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spgist | Index | spghandler | SP-GiST index access method
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(8 rows)
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```
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## 参考
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https://anarazel.de/talks/2018-10-25-pgconfeu-pluggable-storage/pluggable.pdf
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https://commitfest.postgresql.org/22/1283/
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[《PostgreSQL undo多版本存储引擎 zheap测试》](../201809/20180922_01.md)
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[《[未完待续] PostgreSQL 扩展存储引擎介绍 - zheap - 1》](../201803/20180311_02.md)
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<a rel="nofollow" href="http://info.flagcounter.com/h9V1" ><img src="http://s03.flagcounter.com/count/h9V1/bg_FFFFFF/txt_000000/border_CCCCCC/columns_2/maxflags_12/viewers_0/labels_0/pageviews_0/flags_0/" alt="Flag Counter" border="0" ></a>
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## [digoal's 大量PostgreSQL文章入口](https://github.com/digoal/blog/blob/master/README.md "22709685feb7cab07d30f30387f0a9ae")
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## [免费领取阿里云RDS PostgreSQL实例、ECS虚拟机](https://free.aliyun.com/ "57258f76c37864c6e6d23383d05714ea")
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‎201903/20190331_03_pdf_001.pdf‎

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‎201903/20190331_03_pic_001.jpg‎

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‎201903/readme.md‎

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### 文章列表
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----
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##### 20190331_03.md [《PostgreSQL 12 preview - 意义重大改进：增加一层access manager API - 支持 TABLE、INDEX AM(access method) - 为storage pluggable 开路》](20190331_03.md)
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##### 20190331_02.md [《PostgreSQL 12 preview - schema与database的抉择续 - standby drop schema,drop database加速 - standby 延迟优化 - batch to 9.4》](20190331_02.md)
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##### 20190331_01.md [《PostgreSQL 12 preview - partitions pruned at plan time. 原生分区表性能提升23.5倍，已与pg_pathman持平。》](20190331_01.md)
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##### 20190330_09.md [《PostgreSQL 12 preview - DROP OWNED BY xxx 删除xxx的所有对象》](20190330_09.md)

‎README.md‎

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### 所有文档如下
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----
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##### 201903/20190331_03.md [《PostgreSQL 12 preview - 意义重大改进：增加一层access manager API - 支持 TABLE、INDEX AM(access method) - 为storage pluggable 开路》](201903/20190331_03.md)
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##### 201903/20190331_02.md [《PostgreSQL 12 preview - schema与database的抉择续 - standby drop schema,drop database加速 - standby 延迟优化 - batch to 9.4》](201903/20190331_02.md)
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##### 201903/20190331_01.md [《PostgreSQL 12 preview - partitions pruned at plan time. 原生分区表性能提升23.5倍，已与pg_pathman持平。》](201903/20190331_01.md)
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##### 201903/20190330_09.md [《PostgreSQL 12 preview - DROP OWNED BY xxx 删除xxx的所有对象》](201903/20190330_09.md)

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