promql: Fix issue where summation of +/- infinity returns NaN instead of infinity#14362
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…nity Signed-off-by: Charles Korn <charles.korn@grafana.com>
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Just 1 nit: Can we put the test inside functions_test.go? It is a small file and we can add a comment to the test saying why we are testing it separately.
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That was my original intention, but
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Implements the improvements from prometheus/prometheus#14074 prometheus/prometheus#14362
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* MQE: Use kahan in sum aggregation Implements the improvements from prometheus/prometheus#14074 prometheus/prometheus#14362 * Update CHANGELOG
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This fixes an issue with
kahanSumIncwhich would result in NaN being used as the final result when +Inf or -Inf was one of the values added.I've expanded the test coverage of
kahanSumIncto cover these cases and others involving NaN.This does now mean that
kahanSumIncdoes an extra check for Inf at each step. An alternative to this would be to check for +Inf or -Inf when computing the final result (ie. after all the calls tokahanSumInc), but I opted for this as the simplest, least invasive change given how widelykahanSumIncis used.This also revealed what I believe was an incorrect test case in
promql/promqltest/testdata/native_histograms.test, where the stddev and stdvar were incorrectly calculated when a native histogram contained a sample at +Inf.