On Mon, Dec 28, 2020 at 11:20 PM Peter Geoghegan <pg@bowt.ie> wrote:
> > That's a very good result in terms of skipping lazy_vacuum_heap(). How
> > much the table and indexes bloated? Also, I'm curious about that which
> > tests in choose_vacuum_strategy() turned vacuum_heap on: 130 test or
> > test if maintenance_work_mem space is running out? And what was the
> > impact on clearing all-visible bits?
>
> The pgbench_accounts heap table and 3 out of 4 of its indexes (i.e.
> all indexes except "abalance_ruin") had zero growth. They did not even
> become larger by 1 block. As I often say when talking about work in
> this area, this is not a quantitative difference -- it's a qualitative
> difference. (If they grew even a tiny amount, say by only 1 block,
> further growth is likely to follow.)
I forgot to say: I don't know what the exact impact was on the VM bit
setting, but I doubt that it was noticeably worse for the patch. It
cannot have been better, though.
It's inherently almost impossible to keep most of the VM bits set for
long with this workload. Perhaps VM bit setting would be improved with
workloads that have some HOT updates, but as I mentioned this workload
only had non-HOT updates (except in a tiny number of cases where
abalance did not change, just by random luck).
I also forget to say that the maintenance_work_mem test wasn't that
relevant, though I believe it triggered once. maintenance_work_mem was
set very high (5GB).
Here is a link with more details information, in case that is
interesting: https://drive.google.com/file/d/1TqpAQnqb4SMMuhehD8ELpf6Cv9A8ux2E/view?usp=sharing
--
Peter Geoghegan