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How to change Telemetry measurement interval with Gnocchi

Is there any way to change the granularity of Ceilometer sample storage?

With the old non-Gnocchi Ceilometer, I can change the polling interval in pipeline.yaml (now: polling.yaml). When I then run ceilometer sample-list, I can see that samples are taken at the new interval.

With Gnocchi, the equivalent command is gnocchi measures show. However, Gnocchi has its own measurement interval, named granularity, defined by the archive policy:

$ gnocchi archive-policy show medium
| Field               | Value                                                             |
| aggregation_methods | std, count, min, max, sum, mean                                   |
| back_window         | 0                                                                 |
| definition          | - points: 10080, granularity: 0:01:00, timespan: 7 days, 0:00:00  |
|                     | - points: 8760, granularity: 1:00:00, timespan: 365 days, 0:00:00 |
| name                | medium                                                            |

If I want to see samples every 30 seconds rather than the default 1 minute, I need to update the archive policy. I thought anyway. However, Gnocchi doesn't allow me to do that:

$ gnocchi archive-policy update medium -d granularity:30s,points:10080 -d granularity:1h,points:8760       Archive policy medium does not support change: 60.0 granularity interval was changed (HTTP 400)

I found that update_archive_policy() in gnocchi/indexer/ generates this error when the new granularity is different from the old one. So, updating the granularity is simply not allowed. I tried to recreate the archive policy, but I can't delete it since it is in use.