ALTER TABLE ADD COLUMN takes a long time

Question

I was just trying to add a column called \"location\" to a table (main_table) in a database. The command I run was

ALTER TABLE main_table ADD COLUMN location         


        

Answer 1

I think the appropriate answer for this is using a feature like pt-online-schema-change or gh-ost.

We have done migration of over 4 billion rows with this, though it can take upto 10 days, with less than a minute of downtime.

Percona works in a very similar fashion as above

• Create a temp table
• Creates triggers on the first table (for inserts, updates, deletes) so that they are replicated to the temp table
• In small batches, migrate data
• When done, rename table to new table, and drop the other table