[sokoloff]

Not in the context of micro-services, but we ran our production DB for years in a “both N and N+1 work” by following a few simple rules which turn out to be not that restrictive in practice.

Short version: have DB1 hold the transactional data (data generated while running the system). Have DB2a have the release-bound data (data about and connected to the code itself-settings, prices, whatever).

Have DB2a have views onto DB1 tables. Version a code only “knows about” DB2a but any transactional CRUD ops hit the tables on DB1.

Now version b of the code just needs to ship/create a DB2b and both a and b can run in parallel.

If you need to change the shape of DB1 tables, those changes need to be backward compatible (can only add nullable columns, no use of "select *", etc).

There’s a few details about how to make it fully practical, but that’s the gist and we ran than for about 12 years on a moderately heavily trafficked e-commerce site.

[SkyBelow]

Database versioning and backwards compatibility has been something of an upcoming problem where I'm at as we've been getting better at CI/CD. Do you have any recommended resources for different approaches to it, or even some keywords that'll help when searching for such resources?

[rblatz]

This sounds a lot like CQRS

[atonse]

Whoa I love this idea. I usually refer to it as "transactional" (always growing, represents the daily activity, read and write heavy) vs "lookup" data (almost exclusively read, not changed often). But still store them in the same database.

What ends up happening is we end up separating the two more with "cache this one, not that one" rather than two different databases.

I will explore this idea on my next greenfield project, whenever that happens.

[dandigangi]

Ran similar setup to this and worked pretty well!

[atrandom]

This sounds interesting! is there any more detailed write up that you link me to? Thanks!

[sokoloff]

I looked briefly (and I could have sworn I posted our "nine rules" on HN years ago, but I couldn't find it in a quick search).

I'll look again later tonight more thoroughly to see if I've posted the mechanisms and restrictions publicly anywhere before. If I haven't, I'll try to dig it out of our old dev doc system and post them here, but I can't make any promises as the docs I recall are now over a decade old, so I'm not fully sure they exist any more. :)

[sokoloff]

The internal docs for this are not on any of our documentation systems that we've moved to zero-trust (as they're 12 years old and unchanged for 5+ years). I will probably be able to retrieve them when we're back in the offices; shoot me an email (in my profile) and I'll find a way to get something over to you with some significant delay.