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From: Hannu Krosing <hannuk@google.com>
Date: Tue, 8 Apr 2025 09:15:45 +0200
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Subject: Re: Horribly slow pg_upgrade performance with many Large Objects
To: Michael Paquier <michael@paquier.xyz>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Nathan Bossart <nathandbossart@gmail.com>
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I was testing on version 17


On Tue, Apr 8, 2025 at 6:52=E2=80=AFAM Michael Paquier <michael@paquier.xyz=
> wrote:
>
> On Mon, Apr 07, 2025 at 05:25:32PM -0400, Tom Lane wrote:
> > What version are you testing?  We did some work in that area in the
> > v17 cycle (a45c78e32).
>
> I am puzzled by the target version used here, as well.

I was testing on version 17

Here is how you can easily test too (as --binary-upgrade does not dump
the actual data it is ok for the test to not put anything there)

hannuk@db01-c1a:~/work/lo-testing$ createdb -p 5433 lodb
hannuk@db01-c1a:~/work/lo-testing$ psql -p 5433 lodb
psql (17.4 (Ubuntu 17.4-1.pgdg22.04+2))
Type "help" for help.

lodb=3D# insert into pg_largeobject_metadata(oid, lomowner) SELECT i,
16384 FROM generate_series(1, 100_000_000) g(i);
INSERT 0 100000000
Time: 162414.216 ms (02:42.414)
lodb=3D#
\q

hannuk@db01-c1a:~/work/lo-testing$ time pg_dump --data-only -t
pg_largeobject_metadata -p 5433 lodb | gzip >
pg_largeobject_metadata.data.gz
real 0m22.094s
user 0m20.741s
sys 0m2.085s

hannuk@db01-c1a:~/work/lo-testing$ time pg_dump --data-only -t
pg_largeobject_metadata --format=3Dcustom -p 5433 lodb -f
pg_largeobject_metadata.dump
real 0m20.226s
user 0m18.068s
sys 0m0.824s

>  If there is
> more that can be improved, v19 would be the version to consider for
> future improvements at this stage.

If the internal format has changed in 16 the correct way would be to
go through the data-only dump of pg_largeobject_metadata in all cases.
Even for the 100M case where you get the restore in 2 minutes instead
of 100 minutes

hannuk@db01-c1a:~/work/lo-testing$ createdb -p 5434 lodb
hannuk@db01-c1a:~/work/lo-testing$ time pg_restore -p 5434
--exit-on-error --transaction-size=3D1000 --dbname lodb
pg_largeobject_metadata.dump

real 2m2.277s
user 0m2.594s
sys 0m0.549s

And even in case of the user-visible format change in acl format it is
most likely that changing the visible format using some regexp magic,
or even a dedicated function, would still me much faster than creating
all the LOs though creation commands.

------
The commands I used to do the pg_upgrade-like test were

hannuk@db01-c1a:~/work/lo-testing$ time pg_dump --schema-only
--quote-all-identifiers --binary-upgrade --format=3Dcustom
--file=3Dlodb100m.dump -p 5433 lodb
real 1m58.241s
user 0m35.229s
sys 0m17.854s

hannuk@db01-c1a:~/work/lo-testing$ time pg_restore -p 5434
--exit-on-error --transaction-size=3D1000 --dbname lodb lodb100m.dump
real    100m54.878s
user    3m23.885s
sys     20m33.761s

(I left out the --verbose part that pg_upgrade also sets as I did not
want to get 100M lines of  "large object created " messages )

also the postgres server at -p 5434 needs to be started with -b flag
to accept the loading a dump from --binary-upgrade. In Debian/Ubuntu
this can be directly passed to pg_ctlcluster as follows

sudo pg_ctlcluster 17 target -o -b

----
Hannu


> --
> Michael