Prefetch with short TTL?

George (Yorgos) Thessalonikefs george at
Thu Feb 16 08:50:16 UTC 2023

Hi John,

What prefetch does for cached records is to try and refetch the record 
internally (the client still gets the fast cached answer) when a cached 
record is used for the answer and that record's TTL is at the last 10% 
of the original TTL.
This hopefully will update the record in the background and future 
client requests will not notice any resolution delay.
This works best for "popular" records since the prefetch logic needs a 
client query for a non-expired record.

For a record with TTL 60 that means that when the remaining TTL <= 6 and 
a client asks for that record, Unbound will try to update the record in 
the background.

Best regards,
-- Yorgos

On 08/02/2023 23:09, John Horne via Unbound-users wrote:
> Hello,
> Running Unbound 1.16.2, would someone explain what effect the prefetch option
> has with domains with a short TTL (typically 60 seconds) please?
> Thanks,
> John.
> --
> John Horne | Senior Operations Analyst | Technology and Information Services
> University of Plymouth | Drake Circus | Plymouth | Devon | PL4 8AA | UK
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