min duration logging

hey all
trying to find non optimized queries and want to use this logging feature,
however postgresql seems to write every query to log.

my conf is as follows

log_destination = 'csvlog'
logging_collector = on
log_directory = '/usr/local/pgb/pg_log'
log_rotation_size = 100MB
#syslog_facility = 'LOCAL0'
#syslog_ident = 'postgres'
#silent_mode = off
#client_min_messages = debug1
#log_min_messages = warning
#log_min_error_statement = error
log_min_duration_statement = 450
#debug_print_parse = off
#debug_print_rewritten = off
#debug_print_plan = off
#debug_pretty_print = on
#log_checkpoints = off
#log_connections = off
#log_disconnections = off
log_duration = on
#log_error_verbosity = default
#log_hostname = off
#log_line_prefix = ''
#log_lock_waits = off
#log_statement = 'all'
#log_temp_files = -1
#log_timezone = unknown