Once a file is written to disk, it is never written to again

[Josh]

Hello,

Can someone explain to me what is meant by the statement "Once a file is written to disk, it is never written to again" in regard to ROS files? So are the files there forever?

I confused by this.

[NorbertKrupa]

It means that if an update or insert operation happens, the file containing that data doesn't get changed. That data will get added/removed and the data re-written to a new file.

[scutter]

To expand on this a bit more:

- A ROS container is created for every direct COPY or INSERT, and for every Tuple Mover moveout.

- The ROS file is never modified after the initial creation.

- When data is deleted, the ROS container remains untouched. A delete vector (DVWOS/DVROS) is created with the deleted rows and epoch of deletion. The delete rows remain untouched in the ROS container.

- That ROS container remains in place until the ROS container is merged with another container via the Tuple Mover’s mergeout operation, or a partition is dropped, or the table is truncated.

- The fact that ROS containers remain unchanged makes for simple incremental backups since once the ROS’s data files are backed up, they do not need to be backed up again.

—Sharon