Mark Karpilovskij authored Jul 26, 2017 and Daniel Salzman committed Aug 03, 2017

The previous compression algorithm does not compress everything it can
in cases where there are domain names in the data section of a RR, e.g.
when the answer contains

bar.example.com  CNAME  foo.example.com
foo.example.com  A      192.0.0.2

and foo.example.com was not encountered previously, then the second RR
leaves the 'foo' part uncompressed.

The improvement resolves some of these cases by comparing the owner of a new RRset to be written
with the last written dname instead of QNAME. Also, the effectivity was slightly increased
according to benchmarks.