Open Stack

Hi,


1) If you have 30 million instance it means that you have 300 million
instance_system_metadata records
All these records will be downloaded every 6 seconds (in periodic tasks) to
compute_nodes => which means that OpenStack on scale out of box doesn't
work.

If you have 3 million instance the situation is the same (OpenStack doesn't
work). but migration will be done for 1 minute.

So it is maximum 1 minute downtime (in actually non real case).


This change is actually very important because VARCHAR works much much
faster then BLOB (Text) records.
So this is important change and shouldn't be -2.


Best regards,
Boris Pavlovic





On Fri, Oct 25, 2013 at 12:30 AM, Michael Still <mikal at stillhq.com> wrote:

> Hi.
>
> Because I am a grumpy old man I have just -2'ed
> https://review.openstack.org/#/c/39685/ and I wanted to explain my
> rationale. Mostly I am hoping for a consensus to form -- if I am wrong
> then I'll happy remove my vote from this patch.
>
> This patch does the reasonably sensible thing of converting two
> columns from being text to varchar, which reduces their expense to the
> database. Given the data stored is already of limited length, it
> doesn't impact our functionality at all either.
>
> However, when I run it with medium sized (30 million instances)
> databases, the change does cause a 10 minute downtime. I don't
> personally think the change is worth such a large outage, but perhaps
> everyone else disagrees.
>
> Discuss.
>
> Thanks,
> Michael
>
> PS: I could see a more complicated approach where we did these changes
> "in flight" by adding columns, using a periodic task to copy data to
> the new columns, and then dropping the old. That's a lot more
> complicated to implement though.
>
> --
> Rackspace Australia
>
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