Maintained by: NLnet Labs

[Unbound-users] RR ttl in dump_cache

W.C.A. Wijngaards
Tue Jul 7 16:50:22 CEST 2009


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Hi Michael,

On 07/07/2009 04:05 PM, Michael Tokarev wrote:
> I noticed the (relatively) new dump_cache/load_cache
> commands of unbound-control, and started experimenting.
> 
> And immediately come across an.. issue.  The TTL for
> each RR is expressed as time-to-live since "now", it
> is not an expiration time. For this reason it's not
> possible to save the cache and load it back on restart
> for example, because ttl in that case will be invalid.

Yes at the same time the problem but also the reason
people do it.

> I wonder if it's a good idea to use absolute expire
> time in place of TTL in dump/load_cache format.  If
> nothing else, prefixing the field with an equal sign
> will do the trick (=1234567 to mean absolute time,
> 1234567 - current - to mean ttl as it is now).
> 
> And in general, do people use dump/load_cache to
> start with?

Well they want to dump to examine contents.
Want to load to 'hot-start' the cache.  So that the
resolver starts with a full cache.  For that to work
the TTLs have to make the data 'valid'.

I guess that the time of the dump could be stored.
And the readback could make items that used to be valid,
but are now expired, have a TTL of 10-30 seconds (random)
spreading the work to refresh the entries.

Best regards,
   Wouter
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