Online Schema migration in MySQL : When to start? I'm the tech lead of a Social Media SAAS, where we're currently experiencing a big increase in data amount we're storing in our mySQL-database. 

We're having a single MySQL db, and besides many really small tables, we have two tables with approx 500k-1.5m rows. 

Currently, when performing DDL queries (adding new columns to these tables), we have to deal with quite a long execution time (around 4-5 mins).

I started to search for online schema migration tips and found the following:


Alter table on live production databases
mysql change schema on the fly
PT Online Schema Change
OpenARK: Online Alter Table
Facebook's Online Schema change


Although these tactics are worth investigating, I started to feel unconfortable at all: I don't think, that tables with such a low number of rows have to use such advanced methods. (What about really huge tables then?)

So I was wondering, if anyone of you have tips regarding the mysql.cnf itself, or other performance tips for the ddl queries?
I think that Percona's pt-online-schema-change might be a better solution for you as it can do an ALTER with very little downtime. It does, however, require adding a TRIGGER to the table. 

Runnig DDL on your table will lead you into rebuilding your table, mysql is a row based engine so you will suffer the index rebuild this can be quite expensive depending on your engine, table complexity is factor as well.