Setting: URLM_LOG_TRIM_INTERVAL

  How often (in seconds) do you want urlmanager to check the log and
  trim it according to your urlm_max_log_lines and/or urlm_max_log_age
  settings? Default is 3600 seconds (1 hour), which is probably OK for
  most users. If you're in a lot of channels and exchange URLs with lots
  of people, you might want to decrease this to keep the log from growing
  too much.

  Note: urlm_log_trim_interval has no effect unless one or both of the
  urlm_max_log_lines or urlm_max_log_age settings are set to non-zero
  values.

  Note: Even with this setting set to zero, log trimming still occurs
  at startup (unless urlm_log_trim_startup is OFF), and whenever a URL
  is captured. To completely disable log trimming, set both
  urlm_max_log_lines and urlm_max_log_age to zero. With these settings,
  even manual trimming with /urlm_trim_log will do nothing.

  The lower you set this setting, the more CPU and disk access it requires
  (unless you set it to zero, of course). Probably it's a bad idea to
  use a value lower than 60 seconds here, under any conditions.