Request history panel makes SQL panel log extra queries

[x-yuri]

The issue here is that django-debug-toolbar first executes process_response method of every panel, then disables instrumentation, then runs generate_stats. With Request history panel, generate_stats is called when the former processes response, before instrumentation having been disabled.

As a part of generating stats Request panel records session data, which makes an SQL request. The request is recorded by SQL panel, since instrumentation has not yet been disabled. As a result in Debug toolbar I see "1 query in x ms." But when I open SQL panel I see no SQL queries. Supposedly because data for the panel are provided by Request history panel. And by the time Request History panel called generate_stats on SQL panel, no extra queries were executed.

[djsutho]

@x-yuri thanks for the report. Sorry it took me so long to respond. I've pushed up a branch with the added disable_instrumentation() call. Can you install it with:

pip install --no-deps -U git+https://github.com/djsutho/django-debug-toolbar-request-history.git@disable-instrumentation-before-stats-generation

and see if it fixes the issue?

[x-yuri]

Sorry it took me so long to respond

That's okay, and not really long.

Yes, it fixes the issue. And I couldn't see any regressions. I mean, now disable_instrumentation is called twice for each panel. Judging from SQL Panel's code it's okay. But may introduce issues with other panels (third-party ones?).

Speaking of which, doesn't it makes more sense for Debug Toolbar to disable instrumentation first? Or maybe if you collaborate with django-debug-toolbar guys, you might come up with a better solution. Just thinking aloud, your solution is probably good enough.

[djsutho]

It's a good point but from the docs for disable_instrumentation the call should be idempotent so I think it should be okay (if third-party panels follow the docs). If it does turn out to be an issue it should be fairly easy to disable the call (similar to the way generate_stats is).

As for when to call disable_instrumentation I think I had to add the call to generate_stats (which requires the disabling) due to an Panel interface change. From memory the call had to occur at request time but it might be able to be delayed till the stats are required (when selecting a request or displaying a panel). If you want to have a look it might be worth trying to push the generate_stats calls somewhere else and avoid requiring the disable_instrumentation call.

On another note, this issue seems similar (on the request side instead of the response side) so it might be interesting to see how it develops.