[2.1,2.2] cloud-init/curtin http status updates cause high CPU usage

This is a shot in the dark, but could you try the following to see if this improves performance:

    $ sudo maas-region dbshell

    maasdb=# ALTER DATABASE maasdb SET synchronous_commit TO off;

If that doesn't help, then try this:

    maasdb=# ALTER DATABASE maasdb SET commit_delay TO 10000;

If you later want to return to the default settings, you can do:

    maasdb=# ALTER DATABASE maasdb RESET synchronous_commit;
    maasdb=# ALTER DATABASE maasdb RESET commit_delay;

Be sure not to leave the `dbshell` open. I've seen weird behavior in MAAS when this happens (maybe because it's taking up a database connection; not sure).

The other thing you can try is Django connection pooling. Open the MAAS Django settings file, such as:

    $ sudo vi $(dpkg -L maas-region-api | grep settings.py$)

Then find the spot in the file that configures the database. It should look like this:

# Database access configuration.
try:
    with RegionConfiguration.open() as config:
        DATABASES = {
            'default': {
                'ENGINE': 'django.db.backends.postgresql_psycopg2',
                'NAME': config.database_name,
                'USER': config.database_user,
                'PASSWORD': config.database_pass,
                'HOST': config.database_host,
                'PORT': str(config.database_port),
            }
        }

Change it to look like this:

# Database access configuration.
try:
    with RegionConfiguration.open() as config:
        DATABASES = {
            'default': {
                'ENGINE': 'django.db.backends.postgresql_psycopg2',
                'NAME': config.database_name,
                'USER': config.database_user,
                'PASSWORD': config.database_pass,
                'HOST': config.database_host,
                'PORT': str(config.database_port),
                'CONN_MAX_AGE': 600,
            }
        }

Note the addition of CONN_MAX_AGE. This enables Django connection pooling.

Disclaimer: all of the above is at your own risk. While my limited research leads me to believe it might help, I have not tested these options extensively and make no guarantees. But please let me know if it works. ;-)