feat(scrapers.admin): create materialized view and admin page

[grossir]

Concept for #3950

For this to work, the materialized view must be created directly on the DB by running the "query" attribute

For my local database, it looks like this

But, if if connected to the live DB, it would have these rows:

[mlissner]

We haven't used MV's before, so I have questions:

1. I think I asked before, but what do we get from this that a query doesn't get us? I.e., why bother materializing it?

2. How do we run the periodic refresh?

[grossir]

To do this kind of queries we have 3 options

• run the query in a console, or hardcode it in a python string and run it from a postgres interface
• give the query a name, but don't store the results. That's a VIEW. You could then do SELECT * FROM view_name and it will re-execute the query.
• give the query a name, and store the results. That's a MATERIALIZED VIEW

In the case of this query, I don't think a new index would help. I think the slowness comes from joining big tables. Some query optimization may help reduce it more. The raw version takes 10 minutes, prefiltering the docket table by courts that have scrapers takes it down to 3 minutes

Why bother materializing it?

• admin timeout
  If we want to use the admin to look at the results of this query, we risk timing out, as happened with Pghistory admin. I am not sure what the server timeout is, but from Pghistory I think it's about 60 seconds. Having seen that the query takes around 3 minutes to complete, I would expect a timeout.
• waiting (in case it didn't time out)
  Even if it didn't timed out, waiting for 3 minutes each time would make for bad user experience.
  We could try to cache the query, too, for a couple days at least. That would alleviate some problems. I expect a few rows (less than 50) to be returned each time
• django admin hacking
  to take advantage of the django admin HTML templates and ease of navigation, I am using the View (it would work on plain views, which are basically queries, and materialized views) as the concrete table for the django model.

How to refresh it
I expect to check this table a couple times a week. So we could refresh this every 2 or 3 days. We could use a plain cron job, the command is simple REFRESH MATERIALIZED VIEW <name>

Or, we could implement the refresh logic as an async call when accessing the admin page, and send a django admin message (those banners when editing an object) to the user advising to refresh the page in a few minutes

[mlissner]

Hm, in the past we had a script that would send an email with this kind of information, and it ran on a cron job, so I guess this is basically the same thing, but instead of storing the results of the script in an email, this stores the results in the materialized view. Seems fine, I suppose. :)