Re: New IndexAM API controlling index vacuum strategies

On Mon, Mar 1, 2021 at 7:00 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> I think that you're right. However, in practice it isn't harmful
> because has_dead_tuples is only used when "all_visible = true", and
> only to detect corruption (which should never happen). I think that it
> should be fixed as part of this work, though.

Currently the first callsite that calls the new
lazy_vacuum_table_and_indexes() function in the patch
("skip_index_vacuum.patch") skips index vacuuming in exactly the same
way as the second and final lazy_vacuum_table_and_indexes() call site.
Don't we need to account for maintenance_work_mem in some way?

lazy_vacuum_table_and_indexes() should probably not skip index
vacuuming when we're close to exceeding the space allocated for the
LVDeadTuples array. Maybe we should not skip when
vacrelstats->dead_tuples->num_tuples is greater than 50% of
dead_tuples->max_tuples? Of course, this would only need to be
considered when lazy_vacuum_table_and_indexes() is only called once
for the entire VACUUM operation (otherwise we have far too little
maintenance_work_mem/dead_tuples->max_tuples anyway).

--
Peter Geoghegan