How to print application_name in log_line_prefix (using %a)?

Hi, guys,

Could anyone tell me how to specify the application_name as the
log_line_prefix?

According to the manual at
http://www.postgresql.org/docs/9.2/static/runtime-config-logging.html#GUC-APPLICATION-NAME
:

"
application_name (string)

The application_name can be any string of less than NAMEDATALEN characters
(64 characters in a standard build). It is typically set by an application
upon connection to the server. The name will be displayed in the
pg_stat_activity view and included in CSV log entries. It can also be
included in regular log entries via the
log_line_prefix<http://www.postgresql.org/docs/9.2/static/runtime-config-logging.html#GUC-LOG-LINE-PREFIX>parameter.
Only printable ASCII characters may be used in the
application_name value...
"

and also, the manual entry for log_line_prefix (
http://www.postgresql.org/docs/9.2/static/runtime-config-logging.html#GUC-LOG-LINE-PREFIX
)

"
log_line_prefix (string)
This is a printf-style string that is output at the beginning of each log
line. % characters begin "escape sequences" that are replaced with status
information as outlined below...

%a Application name
"

However, I have the following configuration settings in postgresql.conf

application_name = 'mypostgres'
log_line_prefix = '[%a] '

But, my log line is prefixed as "[] " like

[] LOG: 00000: database system was shut down at 2012-10-28 22:15:08 PDT
[] LOCATION: StartupXLOG, xlog.c:6112
[] LOG: 00000: autovacuum launcher started
[] LOCATION: AutoVacLauncherMain, autovacuum.c:407
[] LOG: 00000: database system is ready to accept connections
[] LOCATION: reaper, postmaster.c:2408

Did I miss something?

Thanks a lot!
Tianyin

--
Tianyin XU,
http://cseweb.ucsd.edu/~tixu/