remote: add gate waiting duration metric#18491
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muratclk wants to merge 1 commit intoprometheus:mainfrom
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remote: add gate waiting duration metric#18491muratclk wants to merge 1 commit intoprometheus:mainfrom
muratclk wants to merge 1 commit intoprometheus:mainfrom
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Add a histogram metric prometheus_remote_read_handler_gate_wait_duration_seconds that tracks how long remote read requests wait for the concurrency gate. When the gate's concurrency limit is nearly saturated, operators currently have no way to know that requests are being held up waiting for a free slot. This metric makes that wait visible so operators can decide whether to increase the concurrency limit. The metric is recorded at the call site in the read handler rather than in the gate package itself, keeping the gate as a simple concurrency primitive and avoiding unnecessary API changes. Fixes prometheus#11365 Signed-off-by: muratclk <[email protected]>
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Summary
Add a histogram metric
prometheus_remote_read_handler_gate_wait_duration_secondsthat tracks how long remote read requests wait for the concurrency gate to allow execution.Problem
When the remote read concurrency gate is nearly saturated, operators have no visibility into how long requests are queued waiting for a free slot. The existing
prometheus_remote_read_handler_queriesgauge shows current query count but doesn't reveal queuing latency. Without this signal, operators cannot make informed decisions about when to increase the--storage.remote.read-concurrency-limit.Solution
Record the elapsed time between requesting a gate slot and acquiring it, then observe it in a histogram. The measurement is done at the call site in the read handler (
ServeHTTP) rather than inside the gate package, keeping the gate as a simple concurrency primitive with no metric dependencies.The histogram uses both classic buckets (
prometheus.DefBuckets) and native histogram configuration for forward compatibility.How this helps
Fixes #11365