pg_shdepend
The catalog pg_shdepend records the
dependency relationships between database objects and shared objects,
such as roles. This information allows
PostgreSQL to ensure that those objects are
unreferenced before attempting to delete them.
See also pg_depend,
which performs a similar function for dependencies involving objects
within a single database.
Unlike most system catalogs, pg_shdepend
is shared across all databases of a cluster: there is only one
copy of pg_shdepend per cluster, not
one per database.
Table 52.47. pg_shdepend Columns
| Name | Type | References | Description |
|---|---|---|---|
dbid | oid | | The OID of the database the dependent object is in, or zero for a shared object |
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 (must be a shared catalog) |
refobjid | oid | any OID column | The OID of the specific referenced object |
deptype | char | A code defining the specific semantics of this dependency relationship; see text |
In all cases, a pg_shdepend entry indicates that
the referenced object cannot be dropped without also dropping the dependent
object. However, there are several subflavors identified by
deptype:
SHARED_DEPENDENCY_OWNER (o)The referenced object (which must be a role) is the owner of the dependent object.
SHARED_DEPENDENCY_ACL (a)
The referenced object (which must be a role) is mentioned in the
ACL (access control list, i.e., privileges list) of the
dependent object. (A SHARED_DEPENDENCY_ACL entry is
not made for the owner of the object, since the owner will have
a SHARED_DEPENDENCY_OWNER entry anyway.)
SHARED_DEPENDENCY_POLICY (r)The referenced object (which must be a role) is mentioned as the target of a dependent policy object.
SHARED_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.
SHARED_DEPENDENCY_TABLESPACE (t)The referenced object (which must be a tablespace) is mentioned as the tablespace for a relation that doesn't have storage.
Other dependency flavors might be needed in future. Note in particular that the current definition only supports roles and tablespaces as referenced objects.