Re: pg_upgrade failing for 200+ million Large Objects

> On 11/12/2023, 01:43, "Tom Lane" <tgl@sss.pgh.pa.us <mailto:tgl@sss.pgh.pa.us>> wrote:

> I had initially supposed that in a parallel restore we could
> have child workers also commit after every N TOC items, but was
> soon disabused of that idea. After a worker processes a TOC
> item, any dependent items (such as index builds) might get
> dispatched to some other worker, which had better be able to
> see the results of the first worker's step. So at least in
> this implementation, we disable the multi-command-per-COMMIT
> behavior during the parallel part of the restore. Maybe that
> could be improved in future, but it seems like it'd add a
> lot more complexity, and it wouldn't make life any better for
> pg_upgrade (which doesn't use parallel pg_restore, and seems
> unlikely to want to in future).

I was not able to find email thread which details why we are not using
parallel pg_restore for pg_upgrade. IMHO most of the customer will have single large
database, and not using parallel restore will cause slow pg_upgrade.

I am attaching a patch which enables parallel pg_restore for DATA and POST-DATA part
of dump. It will push down --jobs value to pg_restore and will restore database sequentially.

Benchmarks

{5 million LOs 1 large DB}
Patched {v9}
time pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir ~/upgrade/data/pub --new-datadir ~/data/sub --jobs=20
pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir      17.51s user 65.80s system 35% cpu 3:56.64 total


time pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir ~/upgrade/data/pub --new-datadir ~/data/sub -r
pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir      17.51s user 65.85s system 34% cpu 3:58.39 total


HEAD
time pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir ~/upgrade/data/pub --new-datadir ~/data/sub -r --jobs=20
pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir      53.95s user 82.44s system 41% cpu 5:25.23 total

time pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir ~/upgrade/data/pub --new-datadir ~/data/sub -r
pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir      54.94s user 81.26s system 41% cpu 5:24.86 total



Fix with --jobs propagation to pg_restore {on top of v9}
time pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir ~/upgrade/data/pub --new-datadir ~/data/sub -r --jobs=20
pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir      29.12s user 69.85s system 275% cpu 35.930 total 


Although parallel restore does have small regression in ideal case of pg_upgrade --jobs


Multiple DBs {4 DBs each having 2 million LOs}

Fix with --jobs scheduling
time pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir ~/upgrade/data/pub --new-datadir ~/data/sub -r --jobs=4
pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir      31.80s user 109.52s system 120% cpu 1:57.35 total


Patched {v9}
time pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir ~/upgrade/data/pub --new-datadir ~/data/sub -r --jobs=4
pg_upgrade --old-bindir ~/15/bin --new-bindir ~/install/bin --old-datadir      30.88s user 110.05s system 135% cpu 1:43.97 total


Regards
Sachin