I also have a problem with the history database growing in size so need to reduce this, it has nearly doubled in less than a week.

select pg_size_pretty(pg_database_size('ovirt_engine_history'));

 pg_size_pretty
----------------
 32 GB
(1 row)

 pg_size_pretty
----------------
 56 GB
(1 row)

               Table               |  Size   | External Size 
-----------------------------------+---------+---------------
 vm_interface_samples_history      | 13 GB   | 7813 MB
 vm_disk_samples_history           | 12 GB   | 6688 MB
 vm_samples_history                | 12 GB   | 7823 MB
 vm_disks_usage_samples_history    | 11 GB   | 7557 MB
 vm_disk_hourly_history            | 2210 MB | 899 MB
 vm_interface_hourly_history       | 2123 MB | 1060 MB
 vm_hourly_history                 | 2056 MB | 1086 MB
 vm_disks_usage_hourly_history     | 1735 MB | 1052 MB
 host_interface_samples_history    | 123 MB  | 70 MB
 statistics_vms_users_usage_hourly | 68 MB   | 26 MB
 vm_device_history                 | 53 MB   | 15 MB
 host_interface_configuration      | 33 MB   | 13 MB
 host_interface_hourly_history     | 24 MB   | 12 MB
 vm_configuration                  | 19 MB   | 5720 kB
 vm_interface_configuration        | 14 MB   | 5616 kB
 vm_disk_configuration             | 14 MB   | 5352 kB
 calendar                          | 11 MB   | 3904 kB
 vm_disks_usage_daily_history      | 7400 kB | 5448 kB
 vm_daily_history                  | 7296 kB | 4088 kB
 vm_disk_daily_history             | 7216 kB | 3440 kB
 vm_interface_daily_history        | 6888 kB | 3856 kB
 host_samples_history              | 5048 kB | 2736 kB
 storage_domain_samples_history    | 3016 kB | 1872 kB
 host_hourly_history               | 1176 kB | 584 kB
 storage_domain_hourly_history     | 720 kB  | 456 kB
 statistics_vms_users_usage_daily  | 448 kB  | 304 kB
 users_details_history             | 240 kB  | 80 kB
 host_interface_daily_history      | 176 kB  | 144 kB
 datacenter_configuration          | 176 kB  | 112 kB
 enum_translator                   | 152 kB  | 96 kB
 host_configuration                | 144 kB  | 88 kB
 tag_details                       | 112 kB  | 104 kB
 tag_relations_history             | 104 kB  | 96 kB
 cluster_configuration             | 96 kB   | 88 kB
 storage_domain_daily_history      | 88 kB   | 80 kB
 datacenter_storage_domain_map     | 88 kB   | 80 kB
 host_daily_history                | 88 kB   | 80 kB
 storage_domain_configuration      | 72 kB   | 64 kB
 schema_version                    | 72 kB   | 56 kB
 history_configuration             | 56 kB   | 48 kB
(40 rows)

              Table               |  Size   | External Size 
-----------------------------------+---------+---------------
 vm_disk_samples_history           | 6531 MB | 4499 MB
 vm_interface_samples_history      | 5674 MB | 5674 MB
 vm_samples_history                | 4926 MB | 4926 MB
 vm_disks_usage_samples_history    | 4646 MB | 4646 MB
 vm_disk_hourly_history            | 2735 MB | 1406 MB
 vm_interface_hourly_history       | 2715 MB | 1643 MB
 vm_hourly_history                 | 2560 MB | 1587 MB
 vm_disks_usage_hourly_history     | 2106 MB | 1419 MB
 statistics_vms_users_usage_hourly | 98 MB   | 56 MB
 host_interface_samples_history    | 66 MB   | 66 MB
 vm_device_history                 | 57 MB   | 19 MB
 host_interface_configuration      | 33 MB   | 14 MB
 host_interface_hourly_history     | 28 MB   | 16 MB
 vm_configuration                  | 19 MB   | 6080 kB
 vm_interface_configuration        | 15 MB   | 7248 kB
 vm_disk_configuration             | 15 MB   | 6312 kB
 calendar                          | 11 MB   | 3872 kB
 vm_daily_history                  | 5960 kB | 5960 kB
 vm_disks_usage_daily_history      | 5656 kB | 5656 kB
 vm_interface_daily_history        | 5632 kB | 5632 kB
 vm_disk_daily_history             | 4992 kB | 4992 kB
 storage_domain_samples_history    | 2512 kB | 2512 kB
 host_samples_history              | 1976 kB | 1976 kB
 host_hourly_history               | 1304 kB | 720 kB
 storage_domain_hourly_history     | 1000 kB | 728 kB
 statistics_vms_users_usage_daily  | 544 kB  | 544 kB
 users_details_history             | 208 kB  | 48 kB
 enum_translator                   | 168 kB  | 104 kB
 host_interface_daily_history      | 144 kB  | 144 kB
 datacenter_configuration          | 136 kB  | 72 kB
 host_configuration                | 136 kB  | 80 kB
 host_daily_history                | 104 kB  | 96 kB
 storage_domain_daily_history      | 104 kB  | 96 kB
 schema_version                    | 80 kB   | 56 kB
 tag_details                       | 80 kB   | 72 kB
 tag_relations_history             | 72 kB   | 64 kB
 cluster_configuration             | 64 kB   | 56 kB
 history_configuration             | 56 kB   | 48 kB
 datacenter_storage_domain_map     | 56 kB   | 48 kB
 storage_domain_configuration      | 40 kB   | 32 kB
(40 rows)