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PromQL engine: Delay deletion of __name__ label to the end of the query evaluation - This change allows optionally preserving the `__name__` label via the `label_replace` and `label_join` functions, and helps prevent the dreaded "vector cannot contain metrics with the same labelset" error. - The implementation extends the `Series` and `Sample` structs with a boolean flag indicating whether the `__name__` label should be deleted at the end of the query evaluation. - The `label_replace` and `label_join` functions can still access the value of the `__name__` label, even if it has been previously marked for deletion. If `__name__` is used as target label, it won't be dropped at the end of the query evaluation. - Fixes https://github.com/prometheus/prometheus/issues/11397 - See https://github.com/jcreixell/prometheus/pull/2 for previous discussion, including the decision to create this PR and benchmark it before considering other alternatives (like refactoring `labels.Labels`). - See https://github.com/jcreixell/prometheus/pull/1 for an alternative implementation using a special label instead of boolean flags. - Note: a feature flag `promql-delayed-name-removal` has been added as it changes the behavior of some "weird" queries (see https://github.com/prometheus/prometheus/issues/11397#issuecomment-1451998792) Example (this always fails, as `__name__` is being dropped by `count_over_time`): ``` count_over_time({__name__!=""}[1m]) => Error executing query: vector cannot contain metrics with the same labelset ``` Before: ``` label_replace(count_over_time({__name__!=""}[1m]), "__name__", "count_$1", "__name__", "(.+)") => Error executing query: vector cannot contain metrics with the same labelset ``` After: ``` label_replace(count_over_time({__name__!=""}[1m]), "__name__", "count_$1", "__name__", "(.+)") => count_go_gc_cycles_automatic_gc_cycles_total{instance="localhost:9090", job="prometheus"} 1 count_go_gc_cycles_forced_gc_cycles_total{instance="localhost:9090", job="prometheus"} 1 ... ``` Signed-off-by: Jorge Creixell <jcreixell@gmail.com> --------- Signed-off-by: Jorge Creixell <jcreixell@gmail.com> Signed-off-by: Björn Rabenstein <github@rabenste.in> |
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