tsdb: fix division by zero in stale series compaction#17952
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aknuds1 merged 1 commit intoprometheus:mainfrom Jan 29, 2026
Merged
tsdb: fix division by zero in stale series compaction#17952aknuds1 merged 1 commit intoprometheus:mainfrom
aknuds1 merged 1 commit intoprometheus:mainfrom
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Guard the stale series ratio calculation by checking numSeries > 0 before computing the ratio. This prevents division by zero when the head has no series. Fixes prometheus#17949 Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>
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jesusvazquez
approved these changes
Jan 28, 2026
bwplotka
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Jan 29, 2026
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Which issue(s) does the PR fix:
Fixes #17949
Does this PR introduce a user-facing change?
Summary
Guard the stale series ratio calculation by checking
numSeries > 0before computing the ratio. This prevents division by zero when the head has no series.When
numSeries == 0:numStaleSeries > 0: ratio would be+Inf, incorrectly triggering compactionnumStaleSeries == 0: ratio would beNaN, comparison returns false (safe but semantically incorrect)The fix restructures the condition to check
numSeries > 0before computing the ratio, and moves the ratio calculation inside the condition block.Test plan
TestStaleSeriesCompactionWithZeroSeriesto verifyCompactStaleHead()handles an empty head gracefully