Re: pg_restore with -j > 1 breaks the "clean" phase by not removing dependencies in order

On Mon, Mar 18, 2024 at 9:49 AM Erwin de Haan <erwin(dot)de(dot)haan(at)calcasa(dot)nl>
wrote:

> Hi,
>
> I'm having some trouble getting parallel restores to work. When running
> pg_restore like this:
>
> pg_restore --no-password --host=$MAIN_CLUSTER-pg-cluster --port=5432
> --dbname=$name --jobs=4 --format=d --no-owner --clean --if-exists
> --disable-triggers --role=${name}_owner
> "/temp_data/data-$name-$UNIQUE_SUFFIX"
>
> the restore errors on foreign key constraints while removing tables, is
> there anyway to keep this parallel but have it respect the tree of
> dependencies.
>
> Errors like this:
> pg_restore: error: could not execute query: ERROR: cannot drop table
> public.organisations because other objects depend on it
> DETAIL: constraint fk_groups_organisations_organisation_id on table
> public.groups depends on table public.organisations
> constraint fk_organisation_role_organisations_organisation_id on table
> public.organisation_role depends on table public.organisations
> HINT: Use DROP ... CASCADE to drop the dependent objects too.
> Command was: DROP TABLE IF EXISTS public.organisations;
>
> When executed with --jobs=1 this command works.
>
> So I tried the following: (to restore data and make indices with more than
> one thread but do the initial table creating and cleaning without)
>
> pg_restore --no-password --host=$MAIN_CLUSTER-pg-cluster --port=5432
> --dbname=$name --jobs=1 --section=pre-data --format=d --no-owner --clean
> --if-exists --disable-triggers --role=${name}_owner
> "/temp_data/data-$name-$UNIQUE_SUFFIX"
> pg_restore --no-password --host=$MAIN_CLUSTER-pg-cluster --port=5432
> --dbname=$name --jobs=8 --section=data --format=d --no-owner --clean
> --if-exists --disable-triggers --role=${name}_owner
> "/temp_data/data-$name-$UNIQUE_SUFFIX"
> pg_restore --no-password --host=$MAIN_CLUSTER-pg-cluster --port=5432
> --dbname=$name --jobs=4 --section=post-data --format=d --no-owner --clean
> --if-exists --disable-triggers --role=${name}_owner
> "/temp_data/data-$name-$UNIQUE_SUFFIX"
>
> But now pre-data does not remove the foreign key constraints at all so all
> tables can't be removed by --clean, breaking the whole thing.
>
> Is there some way to make it do this internally? And this doesn't always
> reproduce either, seems like a bit of a race condition because one thread
> is just a bit too fast dropping tables.
>
> We really want the indices to be created after the data gets put in
> because it is much much faster, than doing a schema-only and data-only
> restore.
>
> Kind regards,
>
> Erwin de Haan
>
>
Try "--dbname=template1" instead of "--dbname=$name".

This *always* works for me:
pg_restore -v --jobs=$Threads --clean --create -Fd --dbname=postgres
$BackupRoot/$DbName