[huggyface]

MySQL had some historic issues with schema changes -- adding a column to a table with a few million records could take hours. While it does have a lot of work to do -- it is restructuring every page of the database -- in competitive products such a change takes a minute fraction of the time (limited only by IO performance).

[gizzlon]

But altering a table would still block it? And possible even other tables as well? And take a long time?

Only ever done this in MySQL, where you really can't alter big, live, tables. Well, facebook made an utility for it: http://www.facebook.com/notes/mysql-at-facebook/online-schem...

[jeltz]

Most changes would still block, yes, but at least in PostgreSQL many changes will only block a short time (since they do not require a full table rewrite, only altering the table descirption) and in my experience rewriting a table is generally quick for a decent sized database (tables with a handful of millions of rows).

[jcromartie]

I see. That makes much more sense. Yes, I suppose I'm used to DB servers that are more nimble in that department.