rt46268 contains a correct fix, though for consistency, would it not be
better (and perhaps easier?) to cherry-pick parts of commit 03be5a6b4e6
(Mukund's performance improvements which were not backported to 9.11 and
older branches)?  E.g. like this:

    $ git checkout 03be5a6b4e6 bin/tests/system/filter-aaaa/ns*/*.db{,.in}
    $ git commit

This way the filter-aaaa system test will also start passing again, but
in case we introduce any further changes to it on master, they will be
easier to backport.  It is just a thought, though; rt46268 is good to go
as it is if you like it more.

PS. While v9_10 and v9_11 fail the filter-aaaa system test consistently,
v9_9 failures are intermittent on Robie (and I cannot reproduce them at
all on my machine).  Do you know why this is?