The Internals of PostgreSQL: Process and Memory Architecture
Tags: postgres, apache, apacheage, age
Published: 2023-05-15 07:54:56

This article provides a comprehensive examination of the process architecture and memory architecture of PostgreSQL, with a specific emphasis on its multi-process design. It delves into the various categories of processes and elucidates their respective responsibilities in the administration of the database cluster.

## Process Architecture
PostgreSQL is a relational database management system that operates on a single host and employs a multi-process architecture. These processes work collectively to manage a database cluster, commonly referred to as a "PostgreSQL server." The server comprises several types of processes with distinct roles:

1. The postgres server process serves as the parent process responsible for overseeing the management of the entire database cluster.

2. Backend processes handle queries and statements issued by connected clients, ensuring efficient processing and retrieval of data.

3. Background processes encompass various functionalities, such as performing maintenance tasks like VACUUM and CHECKPOINT processes, vital for effective database management.

4. Replication-related processes enable streaming replication, allowing for data synchronization between multiple instances.

5. Background worker process offers users the flexibility to implement custom operations as per their requirements.

The subsequent subsections will delve into the specifics of the first three types of processes.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/84o3npz4zwoz3j1g1r3l.jpg)

## Postgres Server Process
The postgres server process serves as the primary controller for managing all processes associated with a database cluster. It handles crucial tasks such as allocating shared memory space, initiating background processes, starting replication-related processes, and activating background worker processes when needed.

## Backend Processes
The postgres server process initiates a backend process, commonly referred to as postgres, to handle queries from a single connected client. This backend process establishes communication with the client via a TCP connection and remains active until the client disconnects. PostgreSQL supports concurrent connections from multiple clients, with the maximum number of clients determined by the configuration parameter max_connections (default setting is 100).

## Memory Architecture
To facilitate concurrent access to data, PostgreSQL utilizes shared memory. It implements a cache-based memory management system, which involves storing frequently accessed data in memory to enhance the efficiency of queries. The primary memory region responsible for buffering data pages is the shared buffer pool, a sizable block of shared memory. Each backend process accesses this shared buffer pool to read from and write to data pages.

In addition, PostgreSQL employs the WAL (Write-Ahead Logging) buffer, which is another shared memory area. Its purpose is to temporarily store a copy of the transaction log data before it is written to the WAL file. This mechanism ensures that PostgreSQL can recover from system crashes or other failures without compromising data integrity.