Dashboard: index page is slow

[humitos]

Accessing https://readthedocs.org/dashboard/ while logged in, I can see that it executes 10 SQL queries and they take 2119.93ms. The slowest query here is the one that prefetches the latest build for each of the project the user has access to.

readthedocs.org/readthedocs/projects/querysets.py

Lines 118 to 139 in 1e0ee38

	def prefetch_latest_build(self):
	"""
	Prefetch "latest build" for each project.
	.. note::
	This should come after any filtering.
	"""
	from readthedocs.builds.models import Build
	# Prefetch the latest build for each project.
	subquery = Subquery(
	Build.internal.filter(
	project=OuterRef('project_id')
	).order_by('-date').values_list('id', flat=True)[:1]
	)
	latest_build = Prefetch(
	'builds',
	Build.internal.filter(pk__in=subquery),
	to_attr=self.model.LATEST_BUILD_CACHE,
	)
	return self.prefetch_related(latest_build)

The latest build is used in the template to show when it was built for the last time and also if it has success or failed:

readthedocs.org/readthedocs/templates/projects/project_dashboard_base.html

Lines 69 to 84 in 1e0ee38

	{% with build=project.get_latest_build %}
	<span class="right quiet">
	{% if build %}
	<time class="build-count" datetime="{{ build.date|date:"c" }}" title="{{ build.date|date:"DATETIME_FORMAT" }}">
	<small>{% blocktrans with date=build.date|timesince %}{{ date }} ago{% endblocktrans %}</small>
	</time>
	{% if build.success %}
	<span class="build-state build-state-passing">{% trans "passing" %}</span>
	{% else %}
	<span class="build-state build-state-failing">{% trans "failing" %}</span>
	{# TODO: What whould be show here when "not build.sucess and cancelled"? #}
	{% endif %}
	{% else %}
	<span>{% trans "No builds yet" %}</span>
	{% endif %}