*** a/src/backend/utils/misc/guc-file.l
--- b/src/backend/utils/misc/guc-file.l
***************
*** 45,50 **** static unsigned int ConfigFileLineno;
--- 45,52 ----
  static const char *GUC_flex_fatal_errmsg;
  static sigjmp_buf *GUC_flex_fatal_jmp;
  
+ static void FreeConfigVariable(ConfigVariable *item);
+ 
  /* flex fails to supply a prototype for yylex, so provide one */
  int GUC_yylex(void);
  
***************
*** 151,164 **** ProcessConfigFile(GucContext context)
  	 * file is in the data directory, we can't read it until the DataDir has
  	 * been set.
  	 */
! 	if (DataDir &&
! 		!ParseConfigFile(PG_AUTOCONF_FILENAME, NULL, false, 0, elevel,
! 						 &head, &tail))
  	{
! 		/* Syntax error(s) detected in the file, so bail out */
! 		error = true;
! 		ErrorConfFile = PG_AUTOCONF_FILENAME;
! 		goto cleanup_list;
  	}
  
  	/*
--- 153,218 ----
  	 * file is in the data directory, we can't read it until the DataDir has
  	 * been set.
  	 */
! 	if (DataDir)
  	{
! 		if (!ParseConfigFile(PG_AUTOCONF_FILENAME, NULL, false, 0, elevel,
! 							 &head, &tail))
! 		{
! 			/* Syntax error(s) detected in the file, so bail out */
! 			error = true;
! 			ErrorConfFile = PG_AUTOCONF_FILENAME;
! 			goto cleanup_list;
! 		}
! 	}
! 	/*
! 	 * Pick up only the data_directory if DataDir is not set, which
! 	 * means that the configuration file is read for the first time and
! 	 * PG_AUTOCONF_FILENAME file cannot be read yet. In this case,
! 	 * we shouldn't pick any settings except the data_directory
! 	 * from postgresql.conf because they might be overwritten
! 	 * with the settings in PG_AUTOCONF_FILENAME file which will be
! 	 * read later. OTOH, since it's ensured that data_directory doesn't
! 	 * exist in PG_AUTOCONF_FILENAME file, it will never be overwritten
! 	 * later.
! 	 */
! 	else
! 	{
! 		ConfigVariable *prev = NULL;
! 
! 		for (item = head; item;)
! 		{
! 			ConfigVariable *ptr = item;
! 
! 			item = item->next;
! 			if (strcmp(ptr->name, "data_directory") != 0)
! 			{
! 				if (prev == NULL)
! 					head = ptr->next;
! 				else
! 				{
! 					prev->next = ptr->next;
! 					/*
! 					 * On removing last item in list, we need to update tail
! 					 * to ensure that list will be maintianed.
! 					 */
! 					if (prev->next == NULL)
! 						tail = prev;
! 				}
! 				FreeConfigVariable(ptr);
! 			}
! 			else
! 				prev = ptr;
! 		}
! 
! 		/*
! 		 * Quick exit if data_directory is not present in list.
! 		 *
! 		 * Don't remember when we last successfully loaded the config file in
! 		 * this case because that time will be set soon by subsequent load of
! 		 * the config file.
! 		 */
! 		if (head == NULL)
! 			return;
  	}
  
  	/*
***************
*** 677,683 **** ParseConfigFp(FILE *fp, const char *config_file, int depth, int elevel,
  							*tail_p = prev_item;
  					}
  
! 					pfree(cur_item);
  					break;
  				}
  			}
--- 731,737 ----
  							*tail_p = prev_item;
  					}
  
! 					FreeConfigVariable(cur_item);
  					break;
  				}
  			}
***************
*** 858,863 **** cleanup:
--- 912,932 ----
  }
  
  /*
+  * Free a ConfigVariable
+  */
+ static void
+ FreeConfigVariable(ConfigVariable *item)
+ {
+ 	if (item != NULL)
+ 	{
+ 		pfree(item->name);
+ 		pfree(item->value);
+ 		pfree(item->filename);
+ 		pfree(item);
+ 	}
+ }
+ 
+ /*
   * Free a list of ConfigVariables, including the names and the values
   */
  void
***************
*** 870,879 **** FreeConfigVariables(ConfigVariable *list)
  	{
  		ConfigVariable *next = item->next;
  
! 		pfree(item->name);
! 		pfree(item->value);
! 		pfree(item->filename);
! 		pfree(item);
  		item = next;
  	}
  }
--- 939,945 ----
  	{
  		ConfigVariable *next = item->next;
  
! 		FreeConfigVariable(item);
  		item = next;
  	}
  }
*** a/src/backend/utils/misc/guc.c
--- b/src/backend/utils/misc/guc.c
***************
*** 4339,4344 **** SelectConfigFiles(const char *userDoption, const char *progname)
--- 4339,4351 ----
  		return false;
  	}
  
+ 	/*
+ 	 * Read the configuration file for the first time. This time only
+ 	 * data_directory parameter is picked up to determine the data directory
+ 	 * so that we can read PG_AUTOCONF_FILENAME file next time. Then don't
+ 	 * forget to read the configuration file again later to pick up all the
+ 	 * parameters.
+ 	 */
  	ProcessConfigFile(PGC_POSTMASTER);
  
  	/*