[viraptor]

Why do I get the feeling that you're an op and look down on development people? If that's really true, try to start developing some project and see how you like frequent schema changes, trying to synchronise schemas with peers, resolving relation issues when merging features, etc. On the other hand if you abstract your interaction with data enough, you can change the whole backend later once it's stable and not care about it up-front.

What I hear you saying is unfortunately - it's worse for ops, so noone should use it.

[zzzeek]

> On the other hand if you abstract your interaction with data enough, you can change the whole backend later once it's stable and not care about it up-front.

have to disagree with this. By forcing yourself to work with a data layer so abstracted that you can't even reference whether you're dealing with a JSON document or a set of twelve joinable tables, you're going to write the most tortured and inefficient application. Non trivial applications require leaky abstractions.

[einhverfr]

And you lose the ability to do data constraints well. Put clearly: Declarative data constraints (including referential integrity, but also check constraints and the like) are the single most important features of RDBMS's for most applications.......

[quanticle]

On the other hand, if you abstract your interaction with data enough, you can change the whole backend later once it's stable and not care about it up-front.

This is a conception of data that is more true in theory than it is in practice. In practice, if you want to query your data and efficiently, you'll need to worry about how it's stored. You'll have to worry about the failure cases.

Of course, it is definitely application dependent. If you're just writing a Wordpress-replacement, you can probably choose whatever data store you want and just write an abstraction layer on top of it (especially if you don't care about performance). On the other hand, if you're looking at querying and indexing terabytes (or more) of data, you'll have to work very closely with your data store to extract maximum performance.

[einhverfr]

"If that's really true, try to start developing some project and see how you like frequent schema changes, trying to synchronise schemas with peers, resolving relation issues when merging features, etc. On the other hand if you abstract your interaction with data enough, you can change the whole backend later once it's stable and not care about it up-front."

I can sort of sympathize with this a little. I used to use MySQL for schema prototyping and then move stable stuff to PostgreSQL back when PostgreSQL lacked an alter table drop column capability.

However today, this is less of a factor. Good database engineering is engineering. It's a math intensive discipline. Today I work often with intelligent database design approaches, while trying to allow for agility in higher levels of the app.

Don't get me wrong, NoSQL is great for some things. However it is NEVER a replacement for a good RDBMS where this is needed.

[sausagefeet]

> If that's really true, try to start developing some project and see how you like frequent schema changes, trying to synchronise schemas with peers, resolving relation issues when merging features,

How does something like MongoDB actually help with this, though? Certainly a lack of a schema lets you be more nimble in changing it, but you still have to write code to handle whatever schema you decide rather than letting a battle tested RDBMS handle it. I think NoSQLs have their uses but not forcing correctness on your data as a feature is not one of them. But I also believe in static typing.

[hello_moto]

I've been dev since I graduated. I had been everything else during my intern (dev, qa, test-automation developer, tools dev, build engineer, integration engineer, etc).

Are you saying that Rails schema migration can only solve 10% of your migration needs? That kinda suck bro.

[moe]

Are you saying that Rails schema migration can only solve 10% of your migration needs?

Rails is a bad example here as their primitive migration-system still forces the developer to write those stupid migrations by hand.

Django/South just auto-generates them which removes a huge chore from the daily development workflow.

[hello_moto]

That's excellent! I think it's time for me to learn some Django.

[viraptor]

Migration tools are great once you stop changing the schema very often like it happens when a project starts. This of course depends on the project... if you can have a full design from the start, it's probably going to work too. If you don't know the exact requirements or way to get there - not so much.

[hello_moto]

If you change your schema once every 2-3 days, something wrong with whomever leading the software project. That's like writing a software with zero planning or lack of knowledge for the problem domain.

I don't care if it is a startup or not. Come up with a very simple idea, draw the models in ER diagram, implement that stuff.

It's very hard to imagine that tomorrow suddenly all relationships need to be changed. Even if that is the case, scrap your Repository/Entity model and start from the beginning.

Nothing can help you much if the fundamentals are wrong.

[mrkurt]

Everything else in a software project changes frequently, especially during the early days. "Fundamentals" don't help you know more ahead of time and it's really nice to be able to quickly adjust when you come across something you hadn't anticipated.

I tried building a small side project with Postgres about 8 months ago (after not really doing rdbms stuff for 18 months before) and was amazed at how inflexible it felt, and how much frustration used to seem normal.

[einhverfr]

That's what prototyping and peer review are for,

I write up a schema, send to everyone else on the team, get feedback. If users are invovled get it from them too.... take in all the feedback, write up a new draft, wash, rinse, repeat until running out of shampoo (i.e. feedback).....

Once things are pretty stable, do a prototype, address any oversights, do the real thing.

It's not rocket science.

[lwat]

Could you elaborate please? What were you doing and what made it feel frustrating and inflexible exactly?

[Joakal]

As a startup, change of minds is pretty normal to the point that it's far more better to have the tools to quickly implement it rather than plan/document it well. The only documentation is the general gist behind the database.

If it prototypes well, then further refine it with ER diagrams for future maintenance.

Why is planning everything without validation better than above?

[einhverfr]

Disagree here. Figure an hour of planning saves 10 hrs dev time and 100 hrs bugfixing.

That doesn't mean spending months planning. It does mean doing your best to plan over a few days, then prototype, review, and start implementing. If things change, you now have a clearer idea of the issues and can better address them.

The worst thing you can do is go into development both blind and without important tools you need to make sure that requirements are met--- tools like check constraints, referential integrity, and the like.

[hello_moto]

small to medium changes? find a better migration tools.

large changes? throw away and start over; tools like Rails can help you get up and running really quickly.

I rarely see people go back and fix the mess.

[hammerdr]

To be frank, you're talking out of your ass.

Maintenance takes up about 50% of all IT budget [1]. Most individual pieces of software will spend 2-6 times (considering the average life cycle of an in production software product to be 2-4 years) more money on being maintained than being developed.

Data migration is a massive problem for any organization with data sets at any scale. RDBMS, in general, has gotten in the way of those migrations. People aren't looking at NoSQL just because they cannot sit still but instead are looking to find a better experience with handling data.

I'm not sure if NoSQL is the right answer to that but let's give it a chance and see what happens when people are migrating MongoDB data in 3-4 years.

[1] http://www.zdnet.com/blog/btl/technology-budgets-2010-mainte...

[Devilboy]

If you don't know the requirements to the point that you can't even design a data structure for your project... A schemaless database is NOT going to save you.

[moe]

Ever hear the term "exploratory programming"?