add concepting to comments

Author: wzrdtales

lib/interface/migratorInterface.js

@@ -2,6 +2,27 @@
   * The migrator interface provides the ability to handle all abilities which
   * are needed to successfully modify the DD of your tables.
   * This includes all DDL methods provided by SQL naturally.
+  *
+  * Considering the zero downtime deployment we are handling migrations like
+  * the following:
+  *
+  * ## Data manipulation, the flow:
+  *
+  *  *) The very first step is always a full dump, for the sake of security
+  *
+  * - all operations that are deleting a currently existing column, e.g. renaming a column:
+  *      - 1. duplicate the column
+  *   - if renamed:
+  *      -  1. create a trigger to update both columns
+  *      -  2. disable/delete trigger after successful deployment
+  *   - if deleted:
+  *      - 1. apply steps from the renaming process
+  *      - 2. create a backup of this column (+PK)/table and delete it afterwards (after the successful deployment)
+  * - all operations that modify content
+  *   - 1. Retrieve data to be applied
+  *   - 2. Extract PKs of to be updated rows
+  *   - 3. Create backup of to be updated rows
+  *   - 4. Apply changes 
   */
 
 function dummy() {