Re: Removing more vacuumlazy.c special cases, relfrozenxid optimizations

On Fri, Feb 18, 2022 at 2:11 PM Andres Freund <andres@anarazel.de> wrote:
> I think it'd be good to add a few isolationtest cases for the
> can't-get-cleanup-lock paths. I think it shouldn't be hard using cursors. The
> slightly harder part is verifying that VACUUM did something reasonable, but
> that still should be doable?

We could even just extend existing, related tests, from vacuum-reltuples.spec.

Another testing strategy occurs to me: we could stress-test the
implementation by simulating an environment where the no-cleanup-lock
path is hit an unusually large number of times, possibly a fixed
percentage of the time (like 1%, 5%), say by making vacuumlazy.c's
ConditionalLockBufferForCleanup() call return false randomly. Now that
we have lazy_scan_noprune for the no-cleanup-lock path (which is as
similar to the regular lazy_scan_prune path as possible), I wouldn't
expect this ConditionalLockBufferForCleanup() testing gizmo to be too
disruptive.

-- 
Peter Geoghegan