Try to align runs with frequency #765
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When the agent restarts, we might end up in a situation where we are running a check too often. For example, if a check is configured to run once every 10 minutes, and the check ran 1 minute ago, if we run immediately, we will have two executions within that 10 minute window. Since we have to publish samples once every two minutes, we cannot wait for 9 minutes, because we end up with a gap. Instead, do run immediately to avoid that. But if the check ran 9 minutes ago, we can align with the expectation by waiting for 1 minute instead of a random value. Presumably the check ran 9 minutes ago, and the sample was replicated 7, 5, 3 and 1 minutes ago. If we wait for 1 minute, we would end up running the check when it was expected to run. In order to actually fix this issue the agents would have to persist data across runs. It might be possible to do this by offloading publishing to another service. Fixes: #739 Signed-off-by: Marcelo E. Magallon <marcelo.magallon@grafana.com>
roobre
reviewed
Jul 12, 2024
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| func timeFromNs(ns float64) time.Time { | ||
| sec := int64(math.Floor(ns / 1e9)) | ||
| nsec := int64(math.Mod(ns, 1e9)) | ||
| return time.Unix(sec, nsec) | ||
| } |
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Isn't this redundant? I thought you could just time.Unix(0, ns):
https://go.dev/play/p/zIkG3JFBBvL
The docs state you can:
// It is valid to pass nsec outside the range [0, 999999999].
| return time.Unix(sec, nsec) | ||
| } | ||
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| func computeOffset(offset, frequency time.Duration, t0, now time.Time) time.Duration { |
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Small nit, but I'd suggest naming t0 created instead. t0 suggest some beginning of times, but doesn't seem immediately obvious which one.
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Same about offset, I'm not being able to figure out what that is 🤔
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| // The check was created more than the frequency ago, so we need to | ||
| // compute the time until the next time the check should run. | ||
| // | ||
| // Compute the number of runs since t0, add one for the next run and | ||
| // multiply by the frequency in order to obtain its timestamp. Finally, | ||
| // compute the remaining time until that timestamp. | ||
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| runs := (now.UnixMilli() - t0.UnixMilli()) / frequency.Milliseconds() | ||
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| timeUntilNextRun := t0.Add(time.Duration(runs+1) * frequency).Sub(now) |
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I think I barely grasp what we're doing here, but not enough to try and find gaps in the logic. Looks right but I'm not positive about that.
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When the agent restarts, we might end up in a situation where we are running a check too often. For example, if a check is configured to run once every 10 minutes, and the check ran 1 minute ago, if we run immediately, we will have two executions within that 10 minute window.
Since we have to publish samples once every two minutes, we cannot wait for 9 minutes, because we end up with a gap. Instead, do run immediately to avoid that.
But if the check ran 9 minutes ago, we can align with the expectation by waiting for 1 minute instead of a random value. Presumably the check ran 9 minutes ago, and the sample was replicated 7, 5, 3 and 1 minutes ago. If we wait for 1 minute, we would end up running the check when it was expected to run.
In order to actually fix this issue the agents would have to persist data across runs. It might be possible to do this by offloading publishing to another service.
Fixes: #739