fix(metrics): prevent negative gauge values for buffer metrics - #5467
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fix(metrics): prevent negative gauge values for buffer metrics#5467VedantMadane wants to merge 1 commit into
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LocalMetrics sub/dec could drive buffer size gauges below zero when racey buffer accounting under/over-subtracted (issues fluent#5303, fluent#2712). That produced negative Prometheus series such as fluentd_output_status_buffer_total_bytes. Clamp gauge sub/dec at zero in LocalMetrics, and clamp stage/queue sizes when exporting buffer statistics. Fixes fluent#5303 Signed-off-by: Vedant Madane <6527493+VedantMadane@users.noreply.github.com>
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Which issue(s) this PR fixes:
Fixes #5303
What this PR does / why we need it:
Buffer size gauges (
stage_byte_size,queue_byte_size, and derivedtotal_queued_size) can go negative when Fluentd core under/over-subtracts during concurrent stage/queue transitions. Those values are mirrored by the Prometheus plugin asfluentd_output_status_buffer_total_bytes/fluentd_output_status_buffer_stage_byte_size, which is what #5303 reports.@Watson1978 noted on the issue that the Prometheus plugin only mirrors Fluentd core counters; the drift lives in core (related to the class of races addressed in #2712 / #2734).
This PR:
LocalMetricsgaugesub/decat zero so gauges never go negative under local metrics (the default).statisticsso exporters never publish negative sizes even if an alternate metrics backend returns a negative intermediate value.sub/dec.This does not attempt a full re-audit of every buffer lock path; it stops the user-visible bad export and prevents counter corruption from cascading.
Docs Changes:
N/A
Release Note:
stage_byte_size/queue_byte_size/total_queued_size) under concurrent buffer operations