Changing retention period for metrics

Extending retention period increases the Gnocchi database size insignificantly compared to its default value.

You can change the retention period for metrics through an archive policy. By default, the ceilometer-low-rate and low policies are used to store metrics. Note that you cannot change the metering granularity for these policies.

Prerequisites

To show the details of a particular archive policy

Use the gnocchi archive-policy show command. For example:

# gnocchi --insecure archive-policy show ceilometer-low-rate
+---------------------+---------------------------------------+
| Field               | Value                                 |
+---------------------+---------------------------------------+
| aggregation_methods | rate:mean, mean                       |
| back_window         | 0                                     |
| definition          | - points: 8640, granularity: 0:05:00, |
|                     |   timespan: 30 days, 0:00:00          |
| name                | ceilometer-low-rate                   |
+---------------------+---------------------------------------+

In the output:

  • 8640 points shows how many aggregates will be retained
  • the granularity of 5 minutes defines the time between two aggregates
  • the timespan of 30 days specifies the retention period for aggregates

To sum it up, metrics with the ceilometer-low-rate policy will keep 8640 computed aggregates for one month with 5-minute granularity.

To change the policy definition

Use the gnocchi archive-policy update command. To calculate the correct number of points required for the desired timespan, refer to this formula:

points = timespan \ granularity

For example, to keep aggregates for 2 months with the 5-minute granularity, specify 17280 points:

# gnocchi --insecure archive-policy update ceilometer-low-rate \
-d points:17280,granularity:0:05:00,timespan:60d
+---------------------+----------------------------------------+
| Field               | Value                                  |
+---------------------+----------------------------------------+
| aggregation_methods | rate:mean, mean                        |
| back_window         | 0                                      |
| definition          | - points: 17280, granularity: 0:05:00, |
|                     |   timespan: 60 days, 0:00:00           |
| name                | ceilometer-low-rate                    |
+---------------------+----------------------------------------+