PG_DEPEND

PG_DEPEND records the dependency between database objects. This information allows DROP commands to find which other objects must be dropped by DROP CASCADE or prevent dropping in the DROP RESTRICT case.

See also PG_SHDEPEND, which performs a similar function for dependencies involving objects that are shared across MogDB.

Table 1 PG_DEPEND columns

Name	Type	Reference	Description
classid	oid	PG_CLASS.oid	OID of the system catalog where a dependent object resides
objid	oid	Any OID column	OID of the dependent object
objsubid	integer	-	Column number for a table column (objid and classid refer to the table itself); The value is 0 for all other object types.
refclassid	oid	PG_CLASS.oid	OID of the system catalog where a referenced object resides
refobjid	oid	Any OID column	OID of the referenced object
refobjsubid	integer	-	Column number for a table column (refobjid and refclassid refer to the table itself); 0 for all other object types
deptype	"char"	-	A code defining the specific semantics of this dependency

In all cases, a PG_DEPEND entry indicates that the referenced object cannot be dropped without also dropping the dependent object. However, there are several subflavors identified by deptype:

• DEPENDENCY_NORMAL (n): A normal relationship between separately created objects. The dependent object can be dropped without affecting the referenced object. The referenced object can only be dropped by specifying CASCADE, in which case the dependent object is dropped too. Example: a table column has a normal dependency on its data type.
• DEPENDENCY_AUTO (a): The dependent object can be dropped separately from the referenced object, and should be automatically dropped (regardless of RESTRICT or CASCADE mode) if the referenced object is dropped. Example: a named constraint on a table is made autodependent on the table, so that it will go away if the table is dropped.
• DEPENDENCY_INTERNAL (i): The dependent object was created as part of creation of the referenced object, and is only a part of its internal implementation. A DROP of the dependent object will be disallowed outright (We'll tell the user to issue a DROP against the referenced object, instead). A DROP of the referenced object will be propagated through to drop the dependent object whether CASCADE is specified or not.
• DEPENDENCY_EXTENSION (e): The dependent object is a member of the extension of the referenced object (see PG_EXTENSION). The dependent object can be dropped only via DROP EXTENSION on the referenced object. Functionally this dependency type acts the same as an internal dependency, but it is kept separate for clarity and to simplify GS_DUMP.
• DEPENDENCY_PIN (p): There is no dependent object; this type of entry is a signal that the system itself depends on the referenced object, and so that object must never be deleted. Entries of this type are created only by initdb. The columns for the dependent object contain zeroes.