[ardy42]

> True, but all those migration scripts/patches/table locks add complexity and inconvenience (less agile).

I don't think so. You could say exactly the same thing about maintaining tests for your code. Explicit schemas and constraints (and the effort that goes along with maintaining them) are very much like having tests for your data. They both help ensure that your code actually works when it needs to.

[rooam-dev]

Last time I worked with PostgreSQL, it would lock entire table while adding a new column. Imagine users table, then you have to schedule this kind of altering outside business hours... which impacts devs (they have to stay late and/or come early) and business potentially, it has to wait till next day to have a feature delivered.

All these are trade-offs and everyone decides what is more important for them.

[anarazel]

> it would lock entire table while adding a new column

It does so for the entire << 1ms it takes to add the necessary metadata.

[rooam-dev]

If that's the case, then one less problem to deal with, however I remember it was a matter of several minutes.

[anarazel]

That's only the case if you add a DEFAULT value for the new column. Up until the soon-to-be-released v11 that required updating existing rows. Without a default it's essentially just inserting a single row in a row into an internal catalog table (pg_attribute). With a default in v11, we basically just store the default for a new column out of line, and reference it when the row is read.

In either case a lock has to be acquired on the table, which means if there's a longrunning transaction, you can end up blocking for a while...

[rooam-dev]

Ah, yes, i think that was the case. Thanks for extra details!