From Linuxnetworks
[edit] Use NULL for prio and ttl fields
Each DNS entry in the record table has its own values for time-to-live (TTL) and priority. You can speed up processing of each query in the OpenDBX backend if you set both values in your records table to NULL by default and only set them to an appropriate value if you really need them.
There are two record types where you need different values than NULL in the "prio" fields: For "MX" and "SRV" records. All other record types don't use a priority and therefore NULL is suggested for all of these types.
The same applies to the "ttl" field in each record. There are only a few cases where you really might wish to use different values than the default one you can set by the "default-ttl=..." config option in the pdns.conf file.
