I would add a covered type field to TIMEOUT (c.f. RRSIG).  I also wouldn’t have 
more than
a single timeout per record.  I’m tempted to say a single hash as well.  If 
there is multiple
timeouts per record then the blocks need to be sorted in timeout order.

Covered is there to reduce the number of RR’s that need to be hashed to remove 
a record.
It will also reduce the size of IXFR’s as you don’t need to re-construct a new 
TIMEOUT
record that covers every timeout at a name on each change.

For all records at a name is often more expensive that for all records of type 
covered.
Name servers are optimised for looking up <name,type,class> tuples rather than 
<name,class>
tuples.

Sorting of timeout blocks is so that you can look at the first timeout when 
working out
which TIMEOUT needs to be processed first in a zone.

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: [email protected]

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