Re: Running service migrations during upgrades

[Efraim Flashner]

On Sun, Sep 20, 2020 at 02:39:45PM +0200, Marius Bakke wrote:
> 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?
> 

It looks like Debian has a whole package named "postgres-common" to deal
with updating postgres databases and clusers to newer versions.
https://sources.debian.org/src/postgresql-common/

> 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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Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
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