[Koha-devel] Rolling DB upgrades

[dcook at prosentient.com.au]

I am also skeptical. 

It seems to me that we would have to train every developer on how to write their Perl code and database changes to work with this conceptual model.  

That being said, I am intrigued. I hate downtime as much as the next person.

But how do you propose that the Koha community (and not just your organisation) would make this work? At the moment, the Koha community releases new versions once every month. Some libraries pick those upgrades up automatically, some have sysadmins initiate upgrades, etc. I think we have to assume that no human intervention is a requirement for Koha. So I'm not sure how a 2-step upgrade would work for libraries without sysadmins who were specifically knowledgeable about Koha. 

Happy to hear more though.

David Cook
Software Engineer
Prosentient Systems
Suite 7.03
6a Glen St
Milsons Point NSW 2061
Australia

Office: 02 9212 0899
Online: 02 8005 0595

-----Original Message-----
From: Koha-devel <koha-devel-bounces at lists.koha-community.org> On Behalf Of Julian Maurice
Sent: Wednesday, 3 March 2021 2:56 AM
To: koha-devel at lists.koha-community.org
Subject: Re: [Koha-devel] Rolling DB upgrades

Le 02/03/2021 à 16:00, Joonas Kylmälä a écrit :
> With rolling upgrade we would first create another column with the new 
> name and write & read data to both columns during the 1st step of 
> upgrade, then in 2nd step when all web server nodes are using latest 
> version we could upgrade again to newer version and just delete the 
> old column and start using new one.

Does it mean that the application (Perl) code should be aware of that intermediary state where both columns exist at the same time ? If so, for how long should it be aware of that old database state ?

Does it mean that, for every database schema update, you have to do something like this:
- git reset --hard commit_for_1st_step
- updatedatabase (add new column) && reload starman
- git reset --hard commit_for_2nd_step
- updatedatabase (remove old column) && reload starman ?

Do you know another open source software that allows rolling upgrade ? 
It seems like a great idea, but from what I just read online it looks really hard to do it correctly.

--
Julian Maurice
BibLibre
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