Horton

Re: Lowering the ever-growing heap->pd_lower

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Simon Riggs <simon.riggs@enterprisedb.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, John Naylor <john.naylor@enterprisedb.com>, Tom Lane <tgl@sss.pgh.pa.us>, Mark Dilger <mark.dilger@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-08-04T22:29:03Z
Lists: pgsql-hackers 
On Wed, Aug 4, 2021 at 7:39 AM Robert Haas <robertmhaas@gmail.com> wrote:
> How would it hurt?
>
> It's easy to see the harm caused by not shortening the line pointer
> array when it is possible to do so: we're using up space in the page
> that could have been made free. It's not so obvious to me what the
> downside of shortening it might be.

I think that that's probably true. That in itself doesn't seem like a
good enough reason to commit the patch.

Maybe this really won't be difficult for Matthias. I just want to see
some concrete testing, maybe with pgbench, or with an artificial test
case. Maybe something synthetic that shows a benefit measurable in
on-disk table size. Or at least the absence of any regressions.
Something.

-- 
Peter Geoghegan

Commits

  1. Truncate line pointer array during heap pruning.

  2. Truncate line pointer array during VACUUM.