gpadmin=# \d gp_id
Table "pg_catalog.gp_id"
Column | Type | Modifiers
-------------+----------+-----------
gpname | name | not null
numsegments | smallint | not null
dbid | smallint | not null
content | smallint | not null

Tablespace: "pg_global"

The gp_id system catalog table identifies the Greenplum Database system name and number of segments for the system. It also has local values for the particular database instance (segment or master) on which the table resides. This table is defined in the pg_global tablespace, meaning it is globally shared across all databases in the system.