1. A method for implementation by one or more data processors forming part of at least one computing system, the method comprising: initiating a database operation in an in-memory database that stores persistent data in a secondary storage and has at least one associated log, the database operation involving data having a size above a pre-defined threshold; splitting the data into a plurality of chunks; and executing the database operation by parallelizing each chunk over a plurality of hierarchically arranged threads such that, for each chunk: a parent thread causes each of a plurality of child threads to execute a corresponding consistent change; the child threads each notify the parent thread when they have started their corresponding consistent change; the parent thread starts its own consistent change upon receiving the notifications from all of the child threads that they have started their corresponding consistent change; the parent thread, as part of its consistent change, then writes visibility information and undo and redo log entries in the log; the child threads each notify the parent thread when they have completed their corresponding consistent change; and the parent thread closes its consistent change upon receiving the notifications from all of the child threads that they have completed their corresponding consistent change.