Validate schema name when create.

src/gausskernel/optimizer/commands/schemacmds.cpp

@@ -141,7 +141,10 @@ void CreateSchemaCommand(CreateSchemaStmt* stmt, const char* queryString)
         //@Temp Table. We allow datanode to create pg_temp namespace to enable create namespace stmt by CN to execute on
         // DN
         if (!g_instance.attr.attr_common.allowSystemTableMods && !u_sess->attr.attr_common.IsInplaceUpgrade &&
-            IsReservedName(schemaName) && !IS_PGXC_DATANODE)
+#ifdef ENABLE_MULTIPLE_NODES
+            !IS_PGXC_DATANODE &&
+#endif
+            IsReservedName(schemaName))
             ereport(ERROR,
                 (errcode(ERRCODE_RESERVED_NAME),
                     errmsg("unacceptable schema name \"%s\"", schemaName),

src/test/regress/expected/create_schema.out

@@ -17,6 +17,14 @@ create table abc(
 	b int
 );
 NOTICE:  CREATE TABLE will create implicit sequence "abc_a_seq" for serial column "abc.a"
+--illegal schema name, start with 'pg_'
+create schema pg_error_schema;
+ERROR:  unacceptable schema name "pg_error_schema"
+DETAIL:  The prefix "pg_" is reserved for system schemas.
+--create user will create a schema which name is same as username, so it is also illegal.
+create user pg_error_username password 'test-1234';
+ERROR:  unacceptable user name: fail to create same name schema for user "pg_error_username"
+DETAIL:  The prefix "pg_" is reserved for system schemas.
 drop role samedb_schema_cn_role_02_001;
 drop schema test_ns_schema_1 cascade;
 NOTICE:  drop cascades to 2 other objects

src/test/regress/sql/create_schema.sql

@@ -24,6 +24,11 @@ create table abc(
 	b int
 );
 
+--illegal schema name, start with 'pg_'
+create schema pg_error_schema;
+--create user will create a schema which name is same as username, so it is also illegal.
+create user pg_error_username password 'test-1234';
+
 drop role samedb_schema_cn_role_02_001;
 
 drop schema test_ns_schema_1 cascade;