Also an "old fart", I would recommend postgresql first over any of these other databases. Solve the big data scaling problems when you actually have them. One database server with replication and failover is going to still solve 95-98% or more of the use cases on the web.
It unfortunately doesn’t adequately solve “tweak and update the database software in the middle of the day without requiring downtime” situation very well
We do rolling releases of software all the time but it’s pretty hard for us to do much optimisation of our DB setup without doing it in the middle of the night because of how all this stuff works.
Where I worked in the past they had a rule to only hire DBAs that could manage schema changes and such without downtime. Proper planning up front can mitigate the need to take a lot of those outages.
They still took a window a year for changes where there was no alternative. That is still seems preferable to me to the kinds of ongoing problems that distributed eventually consistent databases produce. You might have better availability numbers, but if customer service has to spend money to fix mistakes caused by data errors I don't know that is better for the business.
Exactly. And also things like rebooting the server, updating the database image, etc. This is why I use HA databases. I can do whatever I like and as long as most of them are still up, traffic continues to be served. If one node is having network issues, no problem. The database is still accessible. And so on.
I would assume you have a staging system to test fixes/updates on, and that rolling out updates would take the form of updating a read slave, then doing a cutover?
The issue we have is that the cutover is super hard to do in a zero-downtime way because we almost always have active connections and you can’t have multiple primaries. There’s tricks like read connections on the replicas but it’s still really hard to coordinate.
Given that Postgres has built in synchronous replication, I feel like it should also have some support for multiple primaries (during a cutover window) to allow better HA support
