doc: Clarify under what circumstances pg_dump needs superuser access.

Inspired by, but different from, a patch from Ivan Lezhnjov IV

diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index ccb76d8af0a5873fc9bdd1aab0bf213002385272..54681a0ba0a858042494f36581d254146b0f06ed 100644 (file)
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -47,8 +47,13 @@ pg_dump dbname > 
    that you can perform this backup procedure from any remote host that has
    access to the database. But remember that pg_dump
    does not operate with special permissions. In particular, it must
-   have read access to all tables that you want to back up, so in
-   practice you almost always have to run it as a database superuser.
+   have read access to all tables that you want to back up, so in order
+   to back up the entire database you almost always have to run it as a
+   database superuser.  (If you do not sufficient privileges to back up the
+   entire database, you can still back up portions of the database to which
+   you do have access using options such as
+   -n schema
+   or -t table.)