Fix reset handling by checking against previous value instead of reset value. #263
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jkschulz
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a team and
igorpeshansky
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igorpeshansky
approved these changes
Jan 12, 2021
modulo one minor formatting comment.
retrieval/series_cache.go
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| // Value of the most recent point seen for the time series. If a new value is | ||
| // less than the previous, then the series has reset. | ||
| previousValue float64 | ||
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| hasReset bool | ||
| resetValue float64 | ||
| resetTimestamp int64 |
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Want to take the opportunity to add a blank line after this one? Or is this how the auto-formatter chose to format it?
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good idea -- added some additional comments too
igorpeshansky
approved these changes
Jan 12, 2021
retrieval/series_cache.go
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| hasReset bool | ||
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| // The value and timestamp of the latest reset. The timestamp is when it | ||
| // occurred and the value is what it was reset to. resetValue will initially |
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Grammar nit: need a comma before the "and".
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There's been a bug in reset handling (since inception) that detects a reset by checking if the current value is less than the initial/reset value, when it should be detecting drops by comparing against the previous value instead. For example, if a series receives values
4->10->6, the existing code will not detect a reset when the value drops from10to6(even though it should), because6</4. It would only detect a reset if the data were e.g.4->10->3, because3<4.Further, this meant that the sidecar could allow at most one reset per time series (so long as it stayed in the cache), because after one reset, the baseline
resetValuewas set to0, and that was what all subsequent values were compared against to identify resets. Since Prometheus counters can't be negative, no additional resets could occur (0 </ 0).Related bugs (internal access only):