Connection errors when sending large amounts of data to browser via a bokeh server

Recently I came across a problem with sending lots of data to a bokeh server, between 20 - 50 MB. The command I used was

bokeh serve data_visualisation --show --args -i path_to_large_file

What would happen is that my plot would render, and then almost instantly a timeout would occur so no communication between the browser and server was possible:

2018-01-05 10:19:58,280 200 GET /data_visualisation (::1) 9227.38ms
2018-01-05 10:19:58,455 101 GET /data_visualisation/ws?bokeh-protocol-version=1.0&bokeh-session-id=jbQmzoBZbYDBDUdi5Ix6QShbAJtAMGPhmKvC1SWjOuwA (::1) 0.87ms
2018-01-05 10:19:58,455 WebSocket connection opened
2018-01-05 10:19:58,456 ServerConnection created
2018-01-05 10:21:28,512 WebSocket connection closed: code=None, reason=None

In the browser console, the following errors where shown:

[bokeh] Lost websocket 0 connection, 1006 ()  connection.js:221
[bokeh] Websocket connection 0 disconnected, will not attempt to reconnect connection.js:105 

The problem was solved by editing tornado.py by changing the rule on line 221 super(BokehTornado, self).__init__(all_patterns) to super(BokehTornado, self).__init__(all_patterns, websocket_max_message_size=50 * 1024 * 1024)

By default, the maximum socket message size is 10MiB for the used version of Tornado, and would disconnect for this reason. A more meaningful error message or the possibility to change this value in bokeh would be appreciated.

Software version info

bokeh==0.12.13 Tornado==4.5.2 python==3.6.3 MacOS High Sierra (10.13.2) Any browser (Chrome (63.0.3239.84) / Safari / Firefox)

[bryevdv]

I’m working on a PR for this right now.

[bryevdv]

@Belloco unfortunately it is not possible to provide a better error message. Those messages originate from the browser, and Tornado respectively, not Bokeh. Bokeh only sees that the connection is closed, it does not get any information about why it was closed.

However, if it is possible to expose websocket_max_message_size as a user configurable option that that’s certainly reasonable. However it is not completely trivial, as that option appears to be new to Tornado 4.5 and Bokeh support tornado >=4.4 so there will have to be some kind of version handling. Are you interested in helping work up a PR for this?