The system catalogs are the place where a relational database management system stores schema metadata, such as information about tables and columns, and internal bookkeeping information. PostgreSQL's system catalogs are regular tables. You can drop and recreate the tables, add columns, insert and update values, and severely mess up your system that way. Normally, one should not change the system
![Chapter 53. System Catalogs](https://cdn-ak-scissors.b.st-hatena.com/image/square/942c169a9546888ebd1837d63ba046041510086f/height=288;version=1;width=512/https%3A%2F%2Fwww.postgresql.org%2Fmedia%2Fimg%2Fabout%2Fpress%2Felephant.png)