Comment by cess11

SDO_POINT(x, y, 0) or SDO_POINT(x, y, NULL) ought to do what you want. Index corruption can be a nasty problem on Postgres too.

You need to decide if and how to perform a rollback, similar to how you would define a down() procedure in migration files. A schema change might imply changes to data, and in that case you might turn off client writes, copy the table, change it, validate, do rename dance, turn on client writes again. If it doesn't it might be much cheaper to operate on a single copy. How does Postgres decide on such strategies automatically?