PG_SHDEPEND

PG_SHDEPEND records the dependency between database objects and shared objects, such as roles. Based on this information, openGauss 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 openGauss. There is only one copy of PG_SHDEPEND per openGauss, 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.

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