Should out-of-band detection or handling be more granular?

[krassowski]

Description

Currently any change to the disk timestamp of the file used by RTC will trigger full reload:

jupyter-collaboration/projects/jupyter-server-ydoc/jupyter_server_ydoc/rooms.py

Lines 336 to 337 in 67453e0

	self._document.source = model["content"]
	self._document.dirty = False

This leads to issues such as:

• Notebook jumps to the first cell on touch (out of band changes) jupyterlab#18100

Reproduce

1. Install jupyter-collaboration
2. Create a test.ipynb notebook with few cells, including interactive outputs, select the last one
3. In terminal run touch test.ipynb
4. See that notebook widget reloads, with cursor jumping to the first cell
5. See that cell outputs were reset and all intermediate state was lost

Expected behavior

• Only the subset of cells that actually changed gets reloaded (rather than a full document).
  • looking at the codebase, I think this may need solving at jupyter-ydoc level
• For touch this should be a no-op
  • this could be solved here as a special case, since we would not want to change the dirty flag either

Context

• JupyterLab version: 4.5.0rc0

[davidbrochart]

For touch this should be a no-op

I think that we should use the file hash to check if the content has changed.

Only the subset of cells that actually changed gets reloaded (rather than a full document)

I think that we could create a new (nbformat) notebook from the content of the file, then compare its cells with the cells of the current YNotebook, and update cells that are different.

[krassowski]

I think that we could create a new (nbformat) notebook from the content of the file, then compare its cells with the cells of the current YNotebook, and update cells that are different.

Should we implement this in jupyter-collaboration, or in jupyter-ydoc? I'm thinking the latter should own it as it is the source of truth about the document structure?

[davidbrochart]

Yes I agree it should be done in jupyter-ydoc, then not only jupyter-collaboration could benefit from it.

[krassowski]

Closing as solved in jupyter-ydoc.