The pg_catalog schema is the standard PostgreSQL meta data and core schema. You will find pre-defined global postgres functions in here as well as useful meta data about your database that is very specific to postgres. This is the schema used by postgres to manage things internally.

What is Pg_catalog in PostgreSQL?

PostgreSQL stores the metadata information about the database and cluster in the schema ‘pg_catalog’. This information is partially used by PostgreSQL itself to keep track of things itself, but it also is presented so external people / processes can understand the inside of the databases too.

What is PG toast?

TOAST is a mechanism PostgreSQL uses to keep physical data rows from exceeding the size of a data block (typically 8KB). … To allow user tables to have rows wider than this, the TOAST mechanism breaks up wide field values into smaller pieces, which are stored “out of line” in a TOAST table associated with the user table.