auth lmdb: split domains table

[miodvallat]

Short description

This is a thought experiment, on the topic of "high database bandwidth caused by updates of domain freshness check timestamps and last notification serial".

A new configuration setting, lmdb-split-domains-table, when set, causes an extra table to be used to store these two fields of the DomainInfo struct. When only these two fields change, only the extra table will get updated. When other fields of DomainInfo change, an up-to-date DomainInfo will be written to the "regular" domains table.

This might be safer than using lmdb-write-notification-update=no.

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)
• no idea what I am doing

[coveralls]

Pull Request Test Coverage Report for Build 21026184422

Details

• 33 of 93 (35.48%) changed or added relevant lines in 1 file are covered.
• 6871 unchanged lines in 83 files lost coverage.
• Overall coverage decreased (-2.6%) to 70.83%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
modules/lmdbbackend/lmdbbackend.cc	33	93	35.48%

Files with Coverage Reduction	New Missed Lines	%
pdns/recursordist/rec-rust-lib/rust/src/bridge.hh	1	0.0%
pdns/recursordist/sortlist.hh	1	75.0%
pdns/dnsdistdist/dnsdist-async.cc	2	83.33%
pdns/dnsname.hh	2	92.47%
pdns/dnstap.cc	2	70.71%
pdns/recursordist/secpoll-recursor.cc	2	51.69%
pdns/sstuff.hh	2	60.67%
pdns/dnsdistdist/dnsdist-carbon.cc	3	62.01%
pdns/ednscookies.hh	3	72.73%
pdns/recursordist/rec-nsspeeds.hh	3	89.41%

Totals
Change from base Build 21011612797:	-2.6%
Covered Lines:	61386
Relevant Lines:	80433

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💛 - Coveralls