Add new OID alias type regrole

The new type has the scope of whole the database cluster so it doesn't
behave the same as the existing OID alias types which have database
scope,
concerning object dependency. To avoid confusion constants of the new
type are prohibited from appearing where dependencies are made involving
it.

Also, add a note to the docs about possible MVCC violation and
optimization issues, which are general over the all reg* types.

Kyotaro Horiguchi

1 files changed, 23 insertions, 4 deletions

diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index da1f25fe285..0cac9935d2d 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -4321,8 +4321,9 @@ SET xmloption TO { DOCUMENT | CONTENT };
     an object identifier.  There are also several alias types for
     <type>oid</>: <type>regproc</>, <type>regprocedure</>,
     <type>regoper</>, <type>regoperator</>, <type>regclass</>,
-    <type>regtype</>, <type>regconfig</>, and <type>regdictionary</>.
-    <xref linkend="datatype-oid-table"> shows an overview.
+    <type>regtype</>, <type>regrole</>, <type>regconfig</>, and
+    <type>regdictionary</>.  <xref linkend="datatype-oid-table"> shows
+    an overview.
    </para>
 
    <para>
@@ -4431,6 +4432,13 @@ SELECT * FROM pg_attribute
        </row>
 
        <row>
+        <entry><type>regrole</></entry>
+        <entry><structname>pg_authid</></entry>
+        <entry>role name</entry>
+        <entry><literal>smithee</></entry>
+       </row>
+
+       <row>
         <entry><type>regconfig</></entry>
         <entry><structname>pg_ts_config</></entry>
         <entry>text search configuration</entry>
@@ -4448,7 +4456,8 @@ SELECT * FROM pg_attribute
     </table>
 
    <para>
-    All of the OID alias types accept schema-qualified names, and will
+    All of the OID alias types for objects grouped by namespace accept
+    schema-qualified names, and will
     display schema-qualified names on output if the object would not
     be found in the current search path without being qualified.
     The <type>regproc</> and <type>regoper</> alias types will only
@@ -4460,7 +4469,7 @@ SELECT * FROM pg_attribute
    </para>
 
    <para>
-    An additional property of the OID alias types is the creation of
+    An additional property of most of the OID alias types is the creation of
     dependencies.  If a
     constant of one of these types appears in a stored expression
     (such as a column default expression or view), it creates a dependency
@@ -4470,7 +4479,17 @@ SELECT * FROM pg_attribute
     understands that the default expression depends on the sequence
     <literal>my_seq</>; the system will not let the sequence be dropped
     without first removing the default expression.
+    <type>regrole</> is the only exception for the property. Constants of this
+    type are not allowed in such expressions.
+   </para>
+
+   <note>
+   <para>
+    The OID alias types do not completely follow transaction isolation
+    rules. The planner also treats them as simple constants, which may
+    result in sub-optimal planning.
    </para>
+   </note>
 
    <para>
     Another identifier type used by the system is <type>xid</>, or transaction