auth: include serial (that is, SOA record) while sending a notify

[omoerbeek]

Short description

This fixes #16129. I'm setting it to Draft status as I:

1. I'm not at home in the auth code
2. A test is missing. I went looking to extend an existing test, but failed to find an existing test testing notify. This might be related to point 1.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document, including the AI Policy, and added a "Signed-off-by" to my commits
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Pull Request Test Coverage Report for Build 22059975061

Details

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• 72 unchanged lines in 16 files lost coverage.
• Overall coverage decreased (-0.01%) to 71.585%

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Files with Coverage Reduction	New Missed Lines	%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.89%
pdns/dnsdistdist/dnsdist-tcp.cc	1	74.68%
pdns/recursordist/aggressive_nsec.cc	2	66.02%
modules/gpgsqlbackend/spgsql.cc	3	68.18%
pdns/axfr-retriever.cc	3	67.47%
pdns/recursordist/recpacketcache.hh	3	91.14%
pdns/recursordist/rec-tcpout.cc	3	82.31%
pdns/dnsdistdist/dnsdist-carbon.cc	4	59.56%
pdns/recursordist/syncres.cc	5	81.58%
pdns/recursordist/test-syncres_cc1.cc	5	79.9%

Totals
Change from base Build 22059357599:	-0.01%
Covered Lines:	129592
Relevant Lines:	166000

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💛 - Coveralls

[mind04]

This feels expensive. This will add at least 2 backend lookups per notified host. With three dual stack namservers this wil add 12 backend queries per notify action.
It also it seems to me that the getSOAUncached() call is redundant and the cached version is sufficient. This will improve the numbers somewhat but I still recommend proper performance testing before this is merged. Especially since there is 0 benefit for powerdns itself.

[omoerbeek]

This feels expensive. This will add at least 2 backend lookups per notified host. With three dual stack namservers this wil add 12 backend queries per notify action. It also it seems to me that the getSOAUncached() call is redundant and the cached version is sufficient. This will improve the numbers somewhat but I still recommend proper performance testing before this is merged. Especially since there is 0 benefit for powerdns itself.

Valid point. Looking at the surrounding code, it does not look easy to reduce the number of SOA lookups. I don't think I'll have an opportunity to do measurements any time of soon, so I'll leave it to auth people to either close this or pick it up.