Dump an extension-member foreign server a foreign table depends on

backup/queries_functions.go

@@ -879,6 +879,15 @@ func (fs ForeignServer) FQN() string {
 
 func GetForeignServers(connectionPool *dbconn.DBConn) []ForeignServer {
 	results := make([]ForeignServer, 0)
+	// A foreign server that belongs to an extension (pg_depend deptype 'e') is
+	// normally skipped, since CREATE EXTENSION is expected to recreate it.
+	// However, gpbackup still dumps the user's foreign tables, which are not
+	// extension members. When such a table depends on an extension-member
+	// server -- e.g. a migration tool registered the server under the FDW
+	// extension with ALTER EXTENSION ... ADD SERVER -- skipping the server
+	// leaves the dumped foreign table unrestorable ("server ... does not
+	// exist"). Also dump an extension-member server when a to-be-dumped foreign
+	// table depends on it, so the backup is self-contained.
 	query := fmt.Sprintf(`
 	SELECT fs.oid,
 		quote_ident(fs.srvname) AS name,
@@ -890,8 +899,16 @@ func GetForeignServers(connectionPool *dbconn.DBConn) []ForeignServer {
 			FROM pg_options_to_table(fs.srvoptions) ORDER BY option_name), ', ') AS options
 	FROM pg_foreign_server fs
 		LEFT JOIN pg_foreign_data_wrapper fdw ON fdw.oid = srvfdw
-	WHERE fs.oid >= %d AND %s
-	ORDER BY fs.oid`, FIRST_NORMAL_OBJECT_ID, ExtensionFilterClause("fs"))
+	WHERE fs.oid >= %d
+		AND (%s
+			OR fs.oid IN (
+				SELECT ft.ftserver
+				FROM pg_foreign_table ft
+					JOIN pg_class c ON c.oid = ft.ftrelid
+					JOIN pg_namespace n ON n.oid = c.relnamespace
+				WHERE %s AND %s))
+	ORDER BY fs.oid`, FIRST_NORMAL_OBJECT_ID, ExtensionFilterClause("fs"),
+		relationAndSchemaFilterClause(), ExtensionFilterClause("c"))
 
 	err := connectionPool.Select(&results, query)
 	gplog.FatalOnError(err)

integration/predata_functions_queries_test.go

@@ -997,6 +997,30 @@ LANGUAGE SQL`)
 			Expect(resultServers).To(HaveLen(1))
 			structmatcher.ExpectStructsToMatchExcluding(&expectedServer, &resultServers[0], "Oid")
 		})
+		It("dumps an extension-member server a foreign table depends on, but not an unreferenced one", func() {
+			// A server registered under an extension (e.g. by a migration tool
+			// via ALTER EXTENSION ... ADD SERVER) is normally filtered out. It
+			// must still be dumped when a non-extension foreign table depends on
+			// it, otherwise that dumped foreign table cannot be restored. A
+			// server no dumped foreign table references stays filtered.
+			testhelper.AssertQueryRuns(connectionPool, "CREATE SERVER referencedserver FOREIGN DATA WRAPPER foreigndatawrapper")
+			testhelper.AssertQueryRuns(connectionPool, "CREATE FOREIGN TABLE public.ref_ftable (i int) SERVER referencedserver")
+			defer testhelper.AssertQueryRuns(connectionPool, "DROP FOREIGN TABLE public.ref_ftable")
+			testhelper.AssertQueryRuns(connectionPool, "ALTER EXTENSION plpgsql ADD SERVER referencedserver")
+			defer testhelper.AssertQueryRuns(connectionPool, "ALTER EXTENSION plpgsql DROP SERVER referencedserver")
+			testhelper.AssertQueryRuns(connectionPool, "CREATE SERVER orphanserver FOREIGN DATA WRAPPER foreigndatawrapper")
+			testhelper.AssertQueryRuns(connectionPool, "ALTER EXTENSION plpgsql ADD SERVER orphanserver")
+			defer testhelper.AssertQueryRuns(connectionPool, "ALTER EXTENSION plpgsql DROP SERVER orphanserver")
+
+			resultServers := backup.GetForeignServers(connectionPool)
+
+			serverNames := make([]string, len(resultServers))
+			for i, server := range resultServers {
+				serverNames[i] = server.Name
+			}
+			Expect(serverNames).To(ContainElement("referencedserver"))
+			Expect(serverNames).ToNot(ContainElement("orphanserver"))
+		})
 	})
 	Describe("GetUserMappings", func() {
 		BeforeEach(func() {