PostgreSQL is one of the finest object-relational databases, and its architecture is process-based instead of thread-based. While almost all the current database systems utilize threads for parallelism, PostgreSQLs process-based architecture was implemented prior to POSIX threads. PostgreSQL launches a process “postmaster” on startup, and after that spans new process whenever a new client connects to [&]

https://www.percona.com/blog/2019/07/30/parallelism-in-postgresql/