lograte after you start postgres

I started postgres with:
$PGHOME/bin/postmaster -D /pg/pg747/data -p 5432  -i >   /pg2/pg747/logs/db_
log  2>&1  &

so my log goes to db_log

now tried rotate log by logrotate by
/pg/pg747/logs/db_log{
        daily
        rotate 60
        copytruncate
        delaycompress
        compress
        notifempty
#       create 600 postgres postgres
}

It is rotating log fine but there some strings I can when I do vi db_log
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^ERROR:  relation "users" does not exist
FATAL:  database "ER" does not exist

Only the first rotated does not show this stings. Any idea how I can fix this problem. My lifekeeper
starts postgres so I don't have any option to start by pipe. So I can not pipe to rotatelog.
Anyone has any idea how I can logrotate once I start postgres and it starts putting all log to one
file.