Description of problem:
when browsing to landing page it takes very long time to fetch the dashboard


the query is:
SELECT SUM(COALESCE(history.cpu_per_socket, 0) * COALESCE (history.number_of_sockets, 0)) AS cpu_total_vms, SUM(CASE WHEN samples.vm_status = 1 THEN COALESCE (history.cpu_per_socket, 0) * COALESCE (history.number_of_sockets, 0) ELSE 0 END ) AS cpu_used_vms, CAST(SUM(COALESCE(history.memory_size_mb, 0.00)) AS float) AS mem_total_vms, CAST(SUM(CASE WHEN samples.vm_status = 1 THEN COALESCE(history.memory_size_mb, 0.00) ELSE 0.00 END) AS float) AS mem_used_vms FROM v4_0_statistics_vms_resources_usage_samples samples INNER JOIN v4_0_configuration_history_vms history ON history.history_id = samples.vm_configuration_version INNER JOIN v4_0_latest_configuration_vms a ON a.vm_id = samples.vm_id WHERE history_datetime >= CURRENT_TIMESTAMP - INTERVAL '5 minute' AND history_datetime <= CURRENT_TIMESTAMP AND samples.history_id IN (SELECT MAX(history_id) FROM v4_0_statistics_vms_resources_usage_samples b GROUP BY vm_id )


Version-Release number of selected component (if applicable):
4.0.7

How reproducible:
100%

Steps to Reproduce:
1. large scale env (39 hosts, 3K vms)
2. fetch the dashboard.
3.

Actual results:
very long response time and sometimes the UI get stuck 

Expected results:
fast response time, stable UI

Additional info: