On 23/05/2019 3:30 am, Dan Davis wrote:
Sure - setting it up is easy. There are hard questions about
database mutations however. If you drop column bar from table Fubar,
then the old code is still querying for buth Fu and Bar:
SELECT id, fu, bar FROM fubar ....
On-premise, this is the case for maybe 10 seconds, tops. *In the
cloud, this could be the case for 30 minutes.*
Are you sure?
My (possibly flawed) understanding is that if you can make the change in
a single transaction, no-one else can see what is happening until it is
committed. Effectively that would be an instantaneous change.
Depending on your data architecture you might need to make some parts
read-only for the 30 minutes prior to committing.
We've decided that this is the developers responsibility, and not the
responsibility of DevOps CI/CD, just like the developer needs to
either use cache-busting techniques when changing JS and CSS, or
educate his users to press Shift-F5 when things go wrong.
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