If you need to perform real-time ALTER TABLE processes on MySQL (InnoDB, TokuDB) tables, a great tool for the job is the Percona Toolkit.

The Percona Toolkit includes a utility (pt-online-schema-change) to perform such a process, without write-locking tables, or having to manually create a temporary table and triggers to synchronize the data during the process.

[codesyntax lang="bash"]

time pt-online-schema-change --host my-awesome-database.example.net --user=user --password=secret --execute --print --no-drop-old-table --alter "DROP INDEX kenny" D=my-database,t=my-table

[/codesyntax]

[codesyntax lang="bash"]

time pt-online-schema-change --hostmy-awesome-database.example.net --user=user --password=secret --execute --print --no-drop-old-table --alter "add source_id int(10) unsigned DEFAULT NULL"D=my-database,t=my-table

[/codesyntax]