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PG Basics - logical structure management (table inheritance, partition table)

2022-06-30 13:04:00 【51CTO】

Table inheritance

What is table inheritance

Create the parent table person, Sub table studen

       
       postgres
       
       =# 
       
       create 
       
       table persons
       
       (
       
postgres
       
       (# name 
       
       text
       
       ,
       
postgres
       
       (# age 
       
       int
       
       ,
       
postgres
       
       (# sex 
       
       boolean
       
       )
       
       ;
       
       CREATE 
       
       TABLE
       
postgres
       
       =# 
       
       create 
       
       table students
       
       (
       
postgres
       
       (# class_no 
       
       int
       
postgres
       
       (# 
       
       )inherits
       
       (persons
       
       )
       
       ;
       
       CREATE 
       
       TABLE
       
postgres
       
       =# 
       
       insert 
       
       into students 
       
       values 
       
       (
       
       ' Zhang San '
       
       ,
       
       15
       
       ,
       
       true
       
       ,
       
       1
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       select  
       
       * 
       
       from persons
       
       ;
       
 name 
       
       | age 
       
       | sex 
       
       ------+-----+-----
       
  Zhang San  
       
       |  
       
       15 
       
       | t
       
       (
       
       1 row
       
       )
       
postgres
       
       =# 
       
       select 
       
       * 
       
       from students
       
       ;
       
 name 
       
       | age 
       
       | sex 
       
       | class_no 
       
       ------+-----+-----+----------
       
  Zhang San  
       
       |  
       
       15 
       
       | t   
       
       |        
       
       1
       
       (
       
       1 row
       
       )
      
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You can see that the sub table inserts data , The parent table is also inserted into the corresponding row .

At the same time, the sub table updates the data , The parent table is also updated .

       
       postgres
       
       =# 
       
       update students 
       
       set age
       
       =
       
       13 
       
       where name
       
       =
       
       ' Zhang San '
       
       ;
       
       UPDATE 
       
       1
       
postgres
       
       =# 
       
       select  
       
       * 
       
       from persons
       
       ;                      
       
 name 
       
       | age 
       
       | sex 
       
       ------+-----+-----
       
  Zhang San  
       
       |  
       
       13 
       
       | t
       
       (
       
       1 row
       
       )
      
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If to persons Table insert data , be studens Watch not visible

Table inheritance rules

（1） When querying the parent table, the data of the word table in the parent table will also be queried , Not the other way around , You just want to query the data of the parent table itself , You only need to add... Before the table name of the query ONLY keyword .

（2） The check constraints and non empty constraints of all parent tables are automatically inherited by all child tables , Other types of constraints （ only , Primary key , Foreign keys ） Will not be inherited

（3） A child table can inherit from multiple parent tables , In this case, it will have the sum of all the parent table fields , If the same field name is listed in multiple parent tables , Then it will merge , The merged field will have all the check constraints of its parent field .

（4） Use DML and DDL Operate parent table , It will also operate on sub tables at the same time , but REINDEX,VACUUM The command does not affect child tables .

Partition table

postgresql Internally, partition tables are implemented through table inheritance . Table partitioning is to divide a large logical table into physical blocks .

The benefits of partitioned tables

（1） Historical data is deleted faster , For example, partition by time , Delete the history partition directly , No partitions may result in VACUUM overload

（2） The performance of some types of queries can be greatly improved , Each partitioned table has its own index , The indexes of highly used partitioned tables may be fully cached in memory , In this way, the efficiency will be much higher .

When to partition

When the size of the table exceeds the physical memory size of the database server .

Steps for creating partition tables

（1） Create the parent table , All partitions inherit from it . There is no data in this table , Do not define any check constraints on it , Unless you want to constrain all partitions .

（2） Create several sub tables , Each is inherited from the main table , Usually these tables do not add any fields ,

（3） Add constraints to the partitioned table , Define the allowed key values for each partition

（4） For each partition , Create an index on key fields

（5） Define a rule or trigger , Insert and redirect the data from the main table to the appropriate partitioned table .

（6） Make sure constraint_exclusion Configuration parameters in postgresql.conf It's open , The purpose is , After opening , If the query where The filter condition of clause matches the constraint condition of partition , Then the query will intelligently query only this partition , No other partitions will be queried .

Steps are as follows

       
       create 
       
       table sales_detail
       
       (
       
product_id 
       
       int 
       
       not 
       
       null
       
       ,
       
price 
       
       numeric
       
       (
       
       12
       
       ,
       
       2
       
       )
       
       ,
       
  amount 
       
       int 
       
       not 
       
       null
       
       ,
       
  sale_date 
       
       date 
       
       not 
       
       null
       
       ,
       
  buyer 
       
       varchar
       
       (
       
       40
       
       )
       
       ,
       
  buyer_countact 
       
       text
       
       )
       
       ;
       
       create 
       
       table sales_detail_y2022m01
       
       (
       
  check 
       
       (sale_date 
       
       > 
       
       DATE '2022-01-01' 
       
       AND sale_date 
       
       < 
       
       DATE '2022-02-01'
       
       )
       
       )INHERITS
       
       (sales_detail
       
       )
       
       ;
       
       create 
       
       table sales_detail_y2022m02
       
       (
       
  check 
       
       (sale_date 
       
       > 
       
       DATE '2022-02-01' 
       
       AND sale_date 
       
       < 
       
       DATE '2022-03-01'
       
       )
       
       )INHERITS
       
       (sales_detail
       
       )
       
       ;
       
       create 
       
       table sales_detail_y2022m03
       
       (
       
  check 
       
       (sale_date 
       
       > 
       
       DATE '2022-03-01' 
       
       AND sale_date 
       
       < 
       
       DATE '2022-04-01'
       
       )
       
       )INHERITS
       
       (sales_detail
       
       )
       
       ;
       
       create index sale_detail_y2022m01_sales_date 
       
       on sales_detail_y2022m01 
       
       (sale_date
       
       )
       
       ;
       
       create index sale_detail_y2022m02_sales_date 
       
       on sales_detail_y2022m02 
       
       (sale_date
       
       )
       
       ;
       
       create index sale_detail_y2022m03_sales_date 
       
       on sales_detail_y2022m03 
       
       (sale_date
       
       )
       
       ;
       
       create 
       
       or replace function sale_detail_insert_trigger
       
       (
       
       )
       
returns trigger 
       
       as $$
       
       begin
       
........
       
end
       
       ;
       
$$
      
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Partitioned tables use triggers to relocate the inserted data to the corresponding partitions .

Partition optimization

constraint_exclusion Skip partitions that do not need to be scanned

Set to off, Each partition word table will be scanned

Declarative partition

Do not create the main table , The method of sub table is to use DDL Way to create

       
       create 
       
       table sales_detail
       
       (
       
product_id 
       
       int 
       
       not 
       
       null
       
       ,
       
price 
       
       numeric
       
       (
       
       12
       
       ,
       
       2
       
       )
       
       ,
       
  amount 
       
       int 
       
       not 
       
       null
       
       ,
       
  sale_date 
       
       date 
       
       not 
       
       null
       
       ,
       
  buyer 
       
       varchar
       
       (
       
       40
       
       )
       
       ,
       
  buyer_countact 
       
       text
       
       )PRATITION 
       
       BY RANGE
       
       (sale_date
       
       )
       
       ;
       
       create 
       
       table sales_detail_y2022m01 PARTITION OF sales_detail
       
FOR 
       
       VALUES 
       
       FROM 
       
       (
       
       '2022-01-01'
       
       ) TO 
       
       (
       
       '2022-02-01'
       
       )
       
       create 
       
       table sales_detail_y2022m02 PARTITION OF sales_detail
       
FOR 
       
       VALUES 
       
       FROM 
       
       (
       
       '2022-02-01'
       
       ) TO 
       
       (
       
       '2022-03-01'
       
       )
      
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