如何计算每小时的平均磁盘空间

Question

I need to calculate the average amount of diskspace used per hour. In a database, I log the diskspace every hour or so (but not always every hour, sometimes more and sometimes less), and I need to calculate the average usage per hour.

I'm stumped, though, since the duration between checks changes. I'm not quite sure the best way to go about doing this.

Additional Details

To clarify:

We have a system setup where diskspace is logged at an interval for billing purposes. The diskspace is charged per byte, but obviously the amount changes throughout the month, so we express it as MB per hour.

In the billing summary, I want to show the average diskspace used in an hour.

At first, it was logging every five minutes. Then I changed it to log per hour. Eventually if there are enough accounts to log, it'll log every two or more hours. But it needs to be normalized to be per hour.

This is done at the end of the month, so there's really no use case of zero data.

Here is some sample data extracted from MySQL. The first query is for the five-minute logs, and the second for the hour logs.

mysql> SELECT FROM_UNIXTIME(date) as date, CONCAT(ROUND(bytes / 1048576, 0), ' MB') AS 'disk usage' FROM host_manager_client_resource_usage WHERE type = 'diskspace' LIMIT 25;
+---------------------+------------+
| date                | disk usage |
+---------------------+------------+
| 2013-03-23 22:40:01 | 28130 MB   |
| 2013-03-23 22:45:01 | 28130 MB   |
| 2013-03-23 22:50:01 | 28116 MB   |
| 2013-03-23 22:55:01 | 28111 MB   |
| 2013-03-23 23:00:01 | 28105 MB   |
| 2013-03-23 23:06:58 | 28089 MB   |
| 2013-03-23 23:10:01 | 28089 MB   |
| 2013-03-23 23:15:01 | 28086 MB   |
| 2013-03-23 23:20:01 | 28086 MB   |
| 2013-03-23 23:25:01 | 28086 MB   |
| 2013-03-23 23:30:01 | 28086 MB   |
| 2013-03-23 23:35:01 | 27644 MB   |
| 2013-03-23 23:40:01 | 26902 MB   |
| 2013-03-23 23:45:01 | 26640 MB   |
| 2013-03-23 23:50:02 | 26640 MB   |
| 2013-03-23 23:55:01 | 26640 MB   |
| 2013-03-24 00:00:01 | 25556 MB   |
| 2013-03-24 00:05:01 | 25556 MB   |
| 2013-03-24 00:10:01 | 24798 MB   |
| 2013-03-24 00:15:01 | 24547 MB   |
| 2013-03-24 00:20:01 | 24547 MB   |
| 2013-03-24 00:25:01 | 20701 MB   |
| 2013-03-24 00:30:01 | 20805 MB   |
| 2013-03-24 00:35:02 | 20807 MB   |
| 2013-03-24 00:40:01 | 20613 MB   |
+---------------------+------------+
25 rows in set (0.00 sec)

mysql> SELECT FROM_UNIXTIME(date) as date, CONCAT(ROUND(bytes / 1048576, 0), ' MB') AS 'disk usage' FROM host_manager_client_resource_usage WHERE duration > 2395 AND type = 'diskspace' ORDER BY id LIMIT 25;
+---------------------+------------+
| date                | disk usage |
+---------------------+------------+
| 2013-03-23 22:40:01 | 28130 MB   |
| 2013-03-28 13:20:37 | 772 MB     |
| 2013-03-28 15:00:01 | 772 MB     |
| 2013-03-28 16:00:02 | 772 MB     |
| 2013-03-28 17:00:01 | 771 MB     |
| 2013-03-28 18:00:01 | 771 MB     |
| 2013-03-28 19:00:01 | 771 MB     |
| 2013-03-28 20:00:01 | 771 MB     |
| 2013-03-28 21:00:01 | 771 MB     |
| 2013-03-28 22:00:01 | 771 MB     |
| 2013-03-28 23:00:01 | 771 MB     |
| 2013-03-29 00:00:01 | 771 MB     |
| 2013-03-29 01:00:01 | 771 MB     |
| 2013-03-29 02:00:01 | 771 MB     |
| 2013-03-29 03:00:01 | 771 MB     |
| 2013-03-29 04:00:01 | 771 MB     |
| 2013-03-29 05:00:01 | 767 MB     |
| 2013-03-29 06:00:01 | 767 MB     |
| 2013-03-29 07:00:01 | 767 MB     |
| 2013-03-29 08:00:01 | 767 MB     |
| 2013-03-29 09:00:01 | 769 MB     |
| 2013-03-29 10:00:01 | 769 MB     |
| 2013-03-29 11:00:01 | 769 MB     |
| 2013-03-29 12:00:01 | 769 MB     |
| 2013-03-29 13:00:01 | 766 MB     |
+---------------------+------------+
25 rows in set (0.00 sec)

Answer 1

Why don't you take the usage at the very beginning, usage at the very end, subtract and divide by the number of hours that passed?

You would have to do a separate subselect to get the first timestamp + usage, last timestamp + usage. Then it is a simple equation like:

(end_usage-start_usage) /
(time_to_sec(timediff(end_timestamp, start_timestamp)) / 3600)