Re: Running service migrations during upgrades

[Alex Sassmannshausen]

Hi Marius,

Your work and thoughts on the SQL upgrades are very interesting.

After the last FOSDEM I wrote up some thoughts about service states and
their backups that you may find interesting.

https://lists.nongnu.org/archive/html/guix-devel/2020-02/msg00002.html

Unfortunately I have not found the time to work on any of this
since. But feel free to steal freely any content that proves useful!

Best wishes,

Alex

Marius Bakke <marius@gnu.org> writes:

> Hello Guix,
>
> Some services require administrator interaction when they are updated.
> The most prominent examples here are MySQL/MariaDB and PostgresQL.
>
> For the former, running 'mysql_upgrade' in-place is generally sufficient
> and fairly safe.
>
> For the latter, the procedure is more involved, and requires making a
> full backup, as well as access to the old _and_ new PostgreSQL
> packages.
>
> There is a patch to update MariaDB here:
>
>   https://issues.guix.gnu.org/43355
>
> Users of mysql-service-type will need to run 'mysql_upgrade' afterwards.
>
> I have been considering adding an AUTO-UPGRADE? parameter of
> mysql-service-type that runs 'mysql_upgrade' as part of the activation
> script.
>
> Another approach is adding a 'herd upgrade' Shepherd action along with a
> news entry describing what to do.  Of course it is possible to do both,
> having 'auto-upgrade?' _and_ a Shepherd action for manual upgrades.
>
> Thoughts?
>
> While that works for MariaDB, I'm not sure what to do about Postgres.
> For those unfamiliar, the procedure for upgrading from PostgreSQL 10
> (current default) to 11 (available in Guix) is roughly:
>
>   sudo cp -a /var/lib/postgresql/data /var/lib/postgresql/data10
>   sudo -u postgres $(guix build postgresql)/bin/pg_upgrade \
>     --old-bindir=$(guix build postgresql@10)/bin \
>     --new-bindir=$(guix build postgresql)/bin \
>     --old-datadir=/var/lib/postgresql/data10 \
>     --new-datadir=/var/lib/postgresql/data
>
> In order to automate it, we need to somehow preserve the "previous"
> version of PostgreSQL so that we can reach it when the major version
> changes.  Or add an 'upgrade-from' parameter to
> postgresql-service-type.
>
> How do other distros deal with this?
>
> On a related note, a 'herd backup' action might be a prerequisite for
> doing such potentially dangerous operations...
>
> I will try to add a 'mysql_upgrade' pass to 'mysql-service-type' in time
> for the MariaDB upgrade, but tips regarding backups, potential pitfalls,
> and especially Postgres welcome.
>
> PS: I'm mostly busy for some time still, but can be reached on #guix or
> by private email if you want my feedback on something.  :-)

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