[dnsdist] Meltdown impact on PowerDNS/dnsdist

[bert hubert]

Hi everybody,

We have done some very tentative measurements on the Linux Meltdown
workaround & impact on DNS performance.

Based on very early measurements we see around a 10% impact in queries per
second for a UDP heavy workload. 

In addition, one largescale user of PowerDNS Authoritative Server on
PostgreSQL suspects the performance problems they see coincided with the
rollout of Meltdown workarounds, but we're still investigating.

Finally, we did a writeup what Meltdown and specifically Spectre actually
are, which you can find on https://ds9a.nl/articles/posts/spectre-meltdown/

We will keep you posted as we learn more!

	Bert