PostgreSQL - Process and Memory Architecture

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PostgreSQL is a popular open-source client/server relational database management system with a multi-process architecture that runs on a single host. The system consists of multiple processes that cooperatively manage one database cluster, which is typically referred to as a 'PostgreSQL server.' The server contains several types of processes, including the postgres server process, backend processes, various background processes, replication-associated processes, and background worker processes.

The postgres server process is the parent of all processes related to a PostgreSQL server. It allocates a shared memory area in memory, starts various background processes, starts replication-associated processes and background worker processes if necessary, and waits for connection requests from clients. Whenever it receives a connection request from a client, it starts a backend process to handle all queries and statements issued by the client.

A backend process is started by the postgres server process and handles all queries issued by one connected client. It communicates with the client by a single TCP connection and terminates when the client gets disconnected. PostgreSQL allows multiple clients to connect simultaneously, and the configuration parameter max_connections controls the maximum number of clients (default is 100).

PostgreSQL has two broad categories of memory architecture: local memory area and shared memory area. The local memory area is allocated by each backend process for its own use and is divided into several sub-areas of fixed or variable sizes. The shared memory area is allocated by a PostgreSQL server when it starts up and is used by all processes of a PostgreSQL server. It is also divided into several fixed-size sub-areas.

In summary, PostgreSQL's process architecture consists of multiple processes that cooperatively manage one database cluster, and its memory architecture consists of a local memory area and a shared memory area. Understanding these architecture components is crucial to understanding how PostgreSQL operates and how to optimize its performance.