Prefetch with short TTL?

Unbound
1

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.

2

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

3

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.

Sorry for the late reply. Thanks for that. We occasionally have a sort of spike
of requests for sites with low TTL values. I was just wondering if this caused
a problem for prefetching or not, given that 10% of the TTL may only be a few
seconds. It seems it is not a problem :slight_smile:

John.