Log duration and statement for slow queries + limiting the number of log files generated

Hello,

I am trying to get postgres 8.4.4 to log the duration and statement of
queries that take longer than 200 ms. I played with the log settings
in postgresql.conf but I still see logs of durations of very fast
statements. Here is my current configuration:

log_min_duration_statement = 200
log_duration = on
log_line_prefix = '<%t> '
log_statement = 'all'

With this configuration I am still getting these in the log files:

<2011-09-02 14:47:19 EDT> LOG: duration: 0.017 ms
<2011-09-02 14:47:19 EDT> LOG: execute <unnamed>: SET SESSION
CHARACTERISTICS AS TRANSACTION READ WRITE
<2011-09-02 14:47:19 EDT> LOG: duration: 0.004 ms
<2011-09-02 14:47:19 EDT> LOG: duration: 0.014 ms
<2011-09-02 14:47:19 EDT> LOG: duration: 0.017 ms
<2011-09-02 14:47:19 EDT> LOG: execute <unnamed>: SET SESSION
CHARACTERISTICS AS TRANSACTION READ ONLY

How do I filter these out?

Also, how do I restrict the maximum number of log files generated to 2
with the assumption that they will roll over when filled?

Thanks,

Alec