Cannot get log_min_duration_statement to work

Question

I have been googling for more than 2 hours, but I am really stuck with this one.
I want PostgreSQL (I am using version 8.4 on Debian) to start logging slow queries only.

Answer 1

Should be:

log_destination = 'csvlog'
logging_collector = on
log_min_duration_statement = 1000
log_line_prefix = '%t %p %r %d %u '### more context
log_statement = 'ddl' ### log schema changes 

Answer 2

log_statement = 'all'

instructs the server to log all statements, simple as that. In addition,

log_duration = on

also instructs the server to log all statements, including duration info.
Change that to

log_statement = none
log_duration = off

No quotes needed. Or comment them out and reload. Then no statement will logged, except those running longer than 1000 ms - instructed by

log_min_duration_statement = 1000

It's all in the excellent manual.