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Document implications of negative observations #658

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Merged
csmarchbanks merged 1 commit into from
May 28, 2021
+18 −2
Merged

Document implications of negative observations #658

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20 changes: 18 additions & 2 deletions prometheus_client/metrics.py
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Original file line number Diff line number Diff line change
Expand Up @@ -441,7 +441,15 @@ def _metric_init(self):
self._created = time.time()

def observe(self, amount):
"""Observe the given amount."""
"""Observe the given amount.

The amount is usually positive or zero. Negative values are
accepted but prevent current versions of Prometheus from
properly detecting counter resets in the sum of
observations. See
https://prometheus.io/docs/practices/histograms/#count-and-sum-of-observations
for details.
"""
self._count.inc(1)
self._sum.inc(amount)

Expand Down Expand Up @@ -550,7 +558,15 @@ def _metric_init(self):
)

def observe(self, amount):
"""Observe the given amount."""
"""Observe the given amount.

The amount is usually positive or zero. Negative values are
accepted but prevent current versions of Prometheus from
properly detecting counter resets in the sum of
observations. See
https://prometheus.io/docs/practices/histograms/#count-and-sum-of-observations
for details.
"""
self._sum.inc(amount)
for i, bound in enumerate(self._upper_bounds):
if amount <= bound:
Expand Down