Ignite should support DROP COLUMN operation for ALTER TABLE command.
1) Drop should only be possible on binary types without schema (see IGNITE-6611). Probably we will need a new option for CREATE TABLE command
2) Drop should not block other operations for a long time. We should synchronously block the table, change meta, then release the lock and let operations continue.
3) Actual data remove should be performed asynchronously in the same way we create index. During this time we should not allow any other modifications to the table
4) Be careful with node stop - we do not want to wait for years for this command to complete.