maria-discuss team mailing list archive

[Artem Russakovskii <archon810@xxxxxxxxx>]

Thanks, Karl. It's pretty shocking that this kind of severe limitation
isn't disclosed and only pointed out in the comments, and that this was the
selected cluster design in the first place. I don't understand how anyone
could use this in production.

Sincerely,
Artem

--
Founder, Android Police <http://www.androidpolice.com>, APK Mirror
<http://www.apkmirror.com/>, Illogical Robot LLC
beerpla.net | @ArtemR <http://twitter.com/ArtemR>


On Wed, Aug 12, 2020 at 1:44 PM Karl Levik <karl.levik@xxxxxxxxx> wrote:

> Hi Artem,
>
> As far as I know based on reading release notes, and in my experience as a
> MariaDB Galera user: Yes, this is still the case. Although more and more
> types of ALTER TABLE statements are now done "online", i.e. they run with
> algorithm=INPLACE | NOCOPY | INSTANT so the table doesn't have to be
> re-built, and therefore they don't necessarily result in the kind of
> long-running, cluster-blocking operations we had in the past.
>
> Still, it would have been nice if there was a way to avoid
> cluster-blocking by DDL in the cases where ALTER TABLE still doesn't run
> "online".
>
> Regards,
> Karl
>
>
> On Wed, 12 Aug 2020 at 21:11, Artem Russakovskii <archon810@xxxxxxxxx>
> wrote:
>
>> Hi,
>>
>> I haven't received a reply to this one. Is someone on the team with
>> knowledge of the cluster able to comment?
>>
>> Thanks.
>>
>> Sincerely,
>> Artem
>>
>> --
>> Founder, Android Police <http://www.androidpolice.com>, APK Mirror
>> <http://www.apkmirror.com/>, Illogical Robot LLC
>> beerpla.net | @ArtemR <http://twitter.com/ArtemR>
>>
>>
>> On Tue, Apr 21, 2020 at 4:15 PM Artem Russakovskii <archon810@xxxxxxxxx>
>> wrote:
>>
>>> Hi,
>>>
>>> On this page
>>> https://mariadb.com/kb/en/mariadb-galera-cluster-known-limitations/, a
>>> user in 2017 pointed out the following:
>>>
>>>
>>> 3 years, 3 months ago Björn Schneider
>>> <https://mariadb.com/kb/user/id/4916>
>>> Schema changes of large tables in Galera
>>> <https://mariadb.com/kb/en/mariadb-galera-cluster-known-limitations/#comment_2704>
>>>
>>> You should be warned that every DDL statement executed on a Galera
>>> cluster will per default BLOCK the complete cluster (not only the table, or
>>> even just the database the table resides in)! This is the default "Total
>>> Order Isolation" (TOI) mode.
>>>
>>> The DDL statements can't be killed - once issued, it will run until
>>> completed or an error occurs.
>>>
>>> Issuing e.g. a column-altering DDL statement on a large table will take
>>> the complete cluster out of commission until every node has completed the
>>> migration. Only some operations (e.g. changing DEFAULT values) are always
>>> short-timed and won't interefere with the cluster's opperations.
>>>
>>> Long-running, cluster-blocking DDL are of course a no-go on a productive
>>> system. To resolve this issue, there are several resulutions; Percona, for
>>> example, provides a script to "online" migrate a table
>>> (pt-online-schema-change), or you can use the "Rolling Schema Upgrade"
>>> (RSU) for data-compatible changes. More about that in the Galera
>>> documentation.
>>>
>>> In my opionion, this behaviour should definitely added as "observation"
>>> to this page - it's definitely not something you'd expect coming from a
>>> "normal" MariaDB/MySQL system.
>>>
>>>
>>> We're considering moving to a cluster environment from a 1 master - 3
>>> slave configuration that has proven inflexible, but such a severe
>>> limitation seems unusable in production.
>>>
>>> Is this still the case in 2020? What is the reasoning behind such an
>>> architectural decision, if so?
>>>
>>> Thank you.
>>>
>>> Sincerely,
>>> Artem
>>>
>>> --
>>> Founder, Android Police <http://www.androidpolice.com>, APK Mirror
>>> <http://www.apkmirror.com/>, Illogical Robot LLC
>>> beerpla.net | @ArtemR <http://twitter.com/ArtemR>
>>>
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>