[Testing] Test the migration speed of Django from the EAV schema to JSONB

[szoupanos]

Given the implementation found at aiida_core/django_jsonb branch, we should take and report the time that is needs for a complete migration of a database of a reasonable size (5m to 10M of nodes).

This is related to issue #2762 and can be inspired by that issue.

Based on the performance we can see if the migration needs improvement.

[szoupanos]

I did a fast check on this using a small database of @giovannipizzi (Giovanni can comment on its contents) that had 63K nodes and 1.3M rows in the attributes table (extras almost empty).

The JSONB migration lasted a bit less than 4,5 mins.

For comparison, the migrations from 0008 to 0025 took 17+ mins (with one of them being particularly slower than the others)

If the migration scales linearly with the number of nodes, an 8M nodes database (with similar contents), will take 9 to 10 hours, which seems a reasonable time.

From a quick look, the migrated attributes seem OK (I saw attributes that make sense, numbers remained numbers and not strings etc)

[szoupanos]

So the migration of the attributes and extras of a 7,3M node database (Davide's) finished in 20 hours.
(django migration: 0034_attributes_extras_settings_json)

More specifically, the timings are the following:
real 1208m12.169s
user 388m30.040s
sys 14m47.921s

And the database contained (rows):
Nodes: 7.351.846
Attributes: 282.505.715
Extras: 3.887.413

The database size decreased from 100GB to 26GB

A mechanical drive was used.