PG_SHDEPEND

PG_SHDEPEND records the dependency between database objects and shared objects, such as roles. Based on this information, MogDB can ensure that those objects are unreferenced before attempting to delete them.

See also PG_DEPEND, which provides a similar function for dependencies involving objects within a single database.

Unlike most system catalogs, PG_SHDEPEND is shared across all databases of MogDB. There is only one copy of PG_SHDEPEND per MogDB, not one per database.

Table 1 PG_SHDEPEND columns

Name	Type	Reference	Description
dbid	oid	PG_DATABASE.oid	OID of the database where a dependent object is (0 for a shared object)
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 is (must be a shared catalog)
refobjid	oid	Any OID column	OID of the referenced object
deptype	"char"	-	Code segment defining the specific semantics of this dependency relationship. See the following for details.
objfile	text	-	Path of a user-defined function library file

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 access control list (ACL) 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_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.