Question: What is the difference between a PostgreSQL cluster and a database?
Answer
In PostgreSQL, the terms 'cluster' and 'database' are often used but they refer to different aspects of the database architecture:
PostgreSQL Cluster
A PostgreSQL cluster refers to a collection of databases that are managed by a single instance of a PostgreSQL server process. The term 'cluster' in this context does not imply multiple servers or high availability (as it might in general IT usage), but rather a group of databases that share a common set of system resources such as memory, background processes, configurations, and catalog information like users and permissions.
When you install PostgreSQL and initialize its environment using the initdb command, you are actually creating a new cluster. All databases created under this setup will share the same PostgreSQL instance.
# Initialize a new PostgreSQL cluster initdb -D /path/to/data/directory
PostgreSQL Database
Within a PostgreSQL cluster, a database is a separate namespace for organizing data. It contains one or more schemas, which in turn include objects like tables, views, functions, etc. Each database is isolated from others; you cannot directly query or join tables across databases within the same cluster.
You can create a new database using the SQL CREATE DATABASE command:
-- Create a new database in a PostgreSQL cluster CREATE DATABASE mydatabase;
Differences Summarized
- Cluster: Refers to the entire PostgreSQL installation including all databases managed by a specific server process.
- Database: A specific, isolated collection of data within the cluster, containing tables, views, and other database objects.
Understanding this distinction is important for managing PostgreSQL effectively, especially when configuring backups, replication, or planning system resources.
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Other Common PostgreSQL Questions (and Answers)
- How can I limit the number of rows updated in a PostgreSQL query?
- How do you limit the number of rows deleted in PostgreSQL?
- How do you use the PARTITION OVER clause in PostgreSQL?
- What are PostgreSQL replication slots and how do they work?
- How can you partition an existing table in PostgreSQL?
- How do you partition a table by multiple columns in PostgreSQL?
- How do you check the replication status in PostgreSQL?
- What are the scaling limits of PostgreSQL?
- How do you scale Azure PostgreSQL?
- How can I improve delete performance in PostgreSQL?
- How can PostgreSQL be auto-scaled?
- What are the best practices for PostgreSQL replication?
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