49.18. pg_depend
The catalogpg_depend records the dependency relationships between database objects. This information allowsDROP commands to find which other objects must be dropped byDROP CASCADE or prevent dropping in theDROP RESTRICT case.
See alsopg_shdepend, which performs a similar function for dependencies involving objects that are shared across a database cluster.
Table 49.18. pg_depend Columns
| Name | Type | References | Description |
|---|---|---|---|
classid | oid | | The OID of the system catalog the dependent object is in |
objid | oid | any OID column | The OID of the specific dependent object |
objsubid | int4 | For a table column, this is the column number (theobjid andclassid refer to the table itself). For all other object types, this column is zero. | |
refclassid | oid | | The OID of the system catalog the referenced object is in |
refobjid | oid | any OID column | The OID of the specific referenced object |
refobjsubid | int4 | For a table column, this is the column number (therefobjid andrefclassid refer to the table itself). For all other object types, this column is zero. | |
deptype | char | A code defining the specific semantics of this dependency relationship; see text |
In all cases, apg_depend entry indicates that the referenced object cannot be dropped without also dropping the dependent object. However, there are several subflavors identified bydeptype:
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
RESTRICTorCASCADEmode) 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 really just a part of its internal implementation. A
DROPof the dependent object will be disallowed outright (we'll tell the user to issue aDROPagainst the referenced object, instead). ADROPof the referenced object will be propagated through to drop the dependent object whetherCASCADEis specified or not. Example: a trigger that's created to enforce a foreign-key constraint is made internally dependent on the constraint'spg_constraintentry.DEPENDENCY_EXTENSION(e)The dependent object is a member of theextension that is the referenced object (see
pg_extension). The dependent object can be dropped only viaDROP EXTENSIONon the referenced object. Functionally this dependency type acts the same as an internal dependency, but it's kept separate for clarity and to simplifypg_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.
Other dependency flavors might be needed in future.