54 lines
2.2 KiB
Markdown
54 lines
2.2 KiB
Markdown
+++
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images = ['images/blog/postgresql.jpg']
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categories = ['Solutions', 'Technology']
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tags = ['Server', 'Database', 'PostgreSQL']
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date = '2022-12-11'
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lastmod = '2022-12-11'
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title = 'Database link with PostgreSQL'
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published = true
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translationKey ='blog-postgresql-database-link'
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slug = 'postgresql-database-link'
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+++
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In PostgreSQL, it is possible to create database links and connect two separate databases, whether they
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reside on the same server or on separate servers, as long as they are accessible over a network.
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<!--more-->
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The used nomenclature is :
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- ```serverorig``` : the source main server
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- ```databaseorig``` : the database name on the source main server
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- ```serverdest``` : the secondary destination server where the database link will be created pointing to ```serverorig```
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- ```schemaorig``` : the schema on the main source server
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- ```schemadest``` : the schema on the secondary destination server
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#### 1. Extension installation
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The first step is to install the extension ```postgres_fdw``` on ```serverdest``` as user ```postgres``` :
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```sql
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CREATE EXTENSION IF NOT EXISTS postgres_fdw;
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```
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#### 2. User creation to access through the database link
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On ```serverorig``` create the user that permits the connection from ```serverdest``` and has access
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to the schema ```schemaorig``` and to the necessary tables. For simplicity we call the user ```userdest``` with
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password ```passworddest``` and it should be able to access the table ```tableorig``` with the desired privileges :
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(```SELECT, INSERT, UPDATE, DELETE```)
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#### 3. Database link creation
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On ```serverdest``` :
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```sql
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CREATE serverorig FOREIGN DATA WRAPPER postgres_fdw OPTIONS (host 'serverorig', port 'portorig', dbname 'databaseorig');
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```
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On ```serverdest``` create the mapping for the user (```myuser```) that should be able to use the database link
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```sql
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CREATE USER MAPPING FOR myuser SERVER serverorig OPTIONS ( user 'userdest' , password 'passworddest');
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```
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#### 5. Import the tables structure from the main schema ad assign the privileges
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On ```serverdest``` :
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```sql
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IMPORT FOREIGN SCHEMA schemaorig LIMIT TO (tableorig) FROM SERVER serverorig INTO schemadest;
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GRANT ALL ON TABLE schemadest.tableorig TO myuser;
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```
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