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 catalogs by hand, there

arealways SQL commands to do that. (For example, <command>CREATE

arenormally SQL commands to do that. (For example, <command>CREATE

DATABASE</command> inserts a row into the

<structname>pg_database</structname> catalog &mdash; and actually

creates the database on disk.) There are some exceptions for

particularly esoteric operations, such as adding index access methods.

particularly esoteric operations, but many of those have been made

available as SQL commands over time, and so the need for direct manipulation

of the system catalogs is ever decreasing.

</para>

<sect1 id="catalogs-overview">