1，database cluster：
database cluster is a collection of databases
2， Shared Memory and Semaphores
sysctl -w kernel.shmmax=17179869184
sysctl -w kernel.shmall=4194304
3，tablespace
4，vacuum
5，write ahead log
6，user and role
7，hot standby
8，后台进程
postgres: logger
postgres: checkpointer
postgres: background writer
postgres: walwriter
postgres: autovacuum launcher
postgres: stats collector
postgres: logical replication launcher
9，relation，page，tuple
10，archiver
11，schema