*** a/doc/src/sgml/config.sgml
--- b/doc/src/sgml/config.sgml
***************
*** 3504,3510 **** local0.*    /var/log/postgresql
              </row>
              <row>
               <entry><literal>%u</literal></entry>
!              <entry>User name</entry>
               <entry>yes</entry>
              </row>
              <row>
--- 3504,3523 ----
              </row>
              <row>
               <entry><literal>%u</literal></entry>
!              <entry>Session user name, typically the user name which was used
!              to authenticate to <productname>PostgreSQL</productname> with,
!              but can be changed by a superuser, see <command>SET SESSION
!              AUTHORIZATION</></entry>
!              <entry>yes</entry>
!             </row>
!             <row>
!              <entry><literal>%U</literal></entry>
!              <entry>Current role name, when set with <command>SET ROLE</>;
!              the current role identifier is relevant for permission checking;
!              Returns 'none' if the current role matches the session user.
!              Note: Log messages from inside <literal>SECURITY DEFINER</>
!              functions will show the calling role, not the effective role
!              inside the <literal>SECURITY DEFINER</> function</entry>
               <entry>yes</entry>
              </row>
              <row>
***************
*** 3731,3737 **** FROM pg_stat_activity;
          (<acronym>CSV</>) format,
          with these columns:
          timestamp with milliseconds,
!         user name,
          database name,
          process ID,
          client host:port number,
--- 3744,3751 ----
          (<acronym>CSV</>) format,
          with these columns:
          timestamp with milliseconds,
!         session user name,
!         current role name,
          database name,
          process ID,
          client host:port number,
***************
*** 3755,3760 **** FROM pg_stat_activity;
--- 3769,3778 ----
          location of the error in the PostgreSQL source code
          (if <varname>log_error_verbosity</> is set to <literal>verbose</>),
          and application name.
+ 
+         For additional details on the definition of the above columns, refer
+         to the documentation for log_line_prefix.
+ 
          Here is a sample table definition for storing CSV-format log output:
  
  <programlisting>
***************
*** 3762,3767 **** CREATE TABLE postgres_log
--- 3780,3786 ----
  (
    log_time timestamp(3) with time zone,
    user_name text,
+   role_name text,
    database_name text,
    process_id integer,
    connection_from text,
*** a/src/backend/commands/variable.c
--- b/src/backend/commands/variable.c
***************
*** 760,765 **** assign_session_authorization(const char *value, bool doit, GucSource source)
--- 760,770 ----
  	return result;
  }
  
+ /*
+  * function to return the stored session username, needed because we
+  * can't do catalog lookups when possibly being called after an error,
+  * eg: from elog.c or part of GUC handling.
+  */
  const char *
  show_session_authorization(void)
  {
***************
*** 885,890 **** assign_role(const char *value, bool doit, GucSource source)
--- 890,900 ----
  	return result;
  }
  
+ /*
+  * function to return the stored role username, needed because we
+  * can't do catalog lookups when possibly being called after an error,
+  * eg: from elog.c or part of GUC handling.
+  */
  const char *
  show_role(void)
  {
*** a/src/backend/utils/error/elog.c
--- b/src/backend/utils/error/elog.c
***************
*** 3,8 ****
--- 3,17 ----
   * elog.c
   *	  error logging and reporting
   *
+  * A few comments about situations where error processing is called:
+  *
+  * We need to be cautious of both a performance hit when logging, since
+  * log messages can be generated at a huge rate if every command is being
+  * logged and we also need to watch out for what can happen when we are
+  * trying to log from an aborted transaction.  Specifically, attempting to
+  * do SysCache lookups and possibly use other usually available backend
+  * systems will fail badly when logging from an aborted transaction.
+  *
   * Some notes about recursion and errors during error processing:
   *
   * We need to be robust about recursive-error scenarios --- for example,
***************
*** 59,64 ****
--- 68,74 ----
  
  #include "access/transam.h"
  #include "access/xact.h"
+ #include "commands/variable.h"
  #include "libpq/libpq.h"
  #include "libpq/pqformat.h"
  #include "mb/pg_wchar.h"
***************
*** 1817,1831 **** log_line_prefix(StringInfo buf, ErrorData *edata)
  				}
  				break;
  			case 'u':
- 				if (MyProcPort)
  				{
! 					const char *username = MyProcPort->user_name;
! 
! 					if (username == NULL || *username == '\0')
! 						username = _("[unknown]");
! 					appendStringInfoString(buf, username);
  				}
  				break;
  			case 'd':
  				if (MyProcPort)
  				{
--- 1827,1850 ----
  				}
  				break;
  			case 'u':
  				{
! 				const char *session_auth = show_session_authorization();
! 				if (*session_auth != '\0')
! 					appendStringInfoString(buf, session_auth);
! 				else
! 					if (MyProcPort)
! 					{
! 						const char *username = MyProcPort->user_name;
! 
! 						if (username == NULL || *username == '\0')
! 							username = _("[unknown]");
! 						appendStringInfoString(buf, username);
! 					}
  				}
  				break;
+ 			case 'U':
+ 				appendStringInfoString(buf, show_role());
+ 				break;
  			case 'd':
  				if (MyProcPort)
  				{
***************
*** 1952,1957 **** appendCSVLiteral(StringInfo buf, const char *data)
--- 1971,1978 ----
  static void
  write_csvlog(ErrorData *edata)
  {
+ 	const char *session_auth = show_session_authorization();
+ 
  	StringInfoData buf;
  	bool		print_stmt = false;
  
***************
*** 1989,1997 **** write_csvlog(ErrorData *edata)
  	appendStringInfoString(&buf, formatted_log_time);
  	appendStringInfoChar(&buf, ',');
  
! 	/* username */
! 	if (MyProcPort)
! 		appendCSVLiteral(&buf, MyProcPort->user_name);
  	appendStringInfoChar(&buf, ',');
  
  	/* database name */
--- 2010,2031 ----
  	appendStringInfoString(&buf, formatted_log_time);
  	appendStringInfoChar(&buf, ',');
  
! 	/* session username, as done for %u */
! 	if (*session_auth != '\0')
! 		appendCSVLiteral(&buf, session_auth);
! 	else
! 		if (MyProcPort)
! 		{
! 			const char *username = MyProcPort->user_name;
! 
! 			if (username == NULL || *username == '\0')
! 				username = _("[unknown]");
! 			appendCSVLiteral(&buf, username);
! 		}
! 	appendStringInfoChar(&buf, ',');
! 
! 	/* current role, same as %U */
! 	appendCSVLiteral(&buf, show_role());
  	appendStringInfoChar(&buf, ',');
  
  	/* database name */