Use a database for statistics

[ewels]

In order to keep the website backend lightweight and simple, I made the dubious decision to store the data for statistics as flat JSON files on the back end. Now that nf-core is getting big, that decision is coming back to bite us. The most obvious example is the Statistics page, which is now super slow to load and starting to break (eg. total Slack users).

Instead of using JSON files, I suggest that we switch to a SQL database like a sane person. We have MySQL available on the server, or if we want to stay simple even a flat file SQLite db would be a big improvement I think. Anything to avoid having to parse huge JSON documents on every page load.

[ewels]

These files are being loaded, parsed and even looped over on every load for the stats page 😱

24M  2 Dec 03:02 nfcore_issue_stats.json
20M  2 Dec 01:01 nfcore_stats.json

It's really amazing that this page loads at all 😅 I added a timer to the code because I knew that it wouldn't scale well, you can see the results in the page footer:

Page generated in 5.21087 seconds.

Code has some nice comments like this one: https://github.com/nf-core/nf-co.re/blob/48e4f5595bf3a4e07f5492080a458d7b68b77a81/public_html/stats.php#L49