52.18. pg_depend
The catalog
pg_depend
records the dependency
relationships 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 a database cluster.
Table 52.18.
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 (the
objid
and
classid
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 (the
refobjid
and
refclassid
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, 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
orCASCADE
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 really just a part of its internal implementation. A
DROP
of the dependent object will be disallowed outright (we'll tell the user to issue aDROP
against the referenced object, instead). ADROP
of the referenced object will be propagated through to drop the dependent object whetherCASCADE
is specified or not. Example: a trigger that's created to enforce a foreign-key constraint is made internally dependent on the constraint'spg_constraint
entry. -
DEPENDENCY_INTERNAL_AUTO
(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
DROP
of the dependent object will be disallowed outright (we'll tell the user to issue aDROP
against the referenced object, instead). While a regular internal dependency will prevent the dependent object from being dropped while any such dependencies remain,DEPENDENCY_INTERNAL_AUTO
will allow such a drop as long as the object can be found by following any of such dependencies. Example: an index on a partition is made internal-auto-dependent on both the partition itself as well as on the index on the parent partitioned table; so the partition index is dropped together with either the partition it indexes, or with the parent index it is attached to. -
DEPENDENCY_EXTENSION
(e
) -
The dependent object is a member of the extension that is the referenced object (see
pg_extension
). The dependent object can be dropped only viaDROP EXTENSION
on the referenced object. Functionally this dependency type acts the same as an internal dependency, but it's kept separate for clarity and to simplify pg_dump . -
DEPENDENCY_AUTO_EXTENSION
(x
) -
The dependent object is not a member of the extension that is the referenced object (and so should not be ignored by pg_dump), but cannot function without it and should be dropped when the extension itself is. The dependent object may be dropped on its own as well.
-
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.