[CELEBORN-2359] Deduplicate # HELP/# TYPE lines in PrometheusServlet output#3734
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afterincomparableyum wants to merge 1 commit into
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[CELEBORN-2359] Deduplicate # HELP/# TYPE lines in PrometheusServlet output#3734afterincomparableyum wants to merge 1 commit into
afterincomparableyum wants to merge 1 commit into
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…output AbstractSource emits a `# HELP` and `# TYPE` line for every metric sample. When a metric family has multiple label sets — like ActiveConnectionCount (per application), RequestSlotsFailedCount (per status code), per-user/app resource consumption, or FlushWorkingQueueSize (per mountpoint) — the same family is exported with repeated `# HELP` and `# TYPE` lines. This violates the Prometheus exposition format. The fix is to override PrometheusServlet.getMetricsSnapshot to keep only the first `# HELP` and `# TYPE` line per metric family while preserving all sample lines, producing valid Prometheus output. I also added a PrometheusServletSuite covering a multi-label-set counter and a distinct gauge.
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Pull request overview
This PR fixes Prometheus exposition format violations by deduplicating repeated # HELP / # TYPE lines emitted per metric sample, ensuring each metric name has only a single HELP/TYPE header while keeping all sample lines.
Changes:
- Override
PrometheusServlet.getMetricsSnapshotto filter duplicate# HELP/# TYPElines per metric name. - Add a
PrometheusServletSuitetest covering a multi-label-set counter plus a separate gauge.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| service/src/main/scala/org/apache/celeborn/common/metrics/sink/PrometheusServlet.scala | Adds post-processing of the raw snapshot to deduplicate HELP/TYPE header lines. |
| service/src/test/scala/org/apache/celeborn/common/metrics/sink/PrometheusServletSuite.scala | Adds coverage ensuring HELP/TYPE lines appear only once for multi-label-set metrics. |
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| raw.linesIterator.foreach { | ||
| case line @ header(kind, metric) => | ||
| val key = s"$kind\t$metric" | ||
| if (!seen.contains(key)) { | ||
| out.append(line).append('\n') | ||
| seen += key | ||
| } | ||
| case line => | ||
| out.append(line).append('\n') | ||
| } |
| source.addGauge("Gauge1") { () => 1000 } | ||
|
|
||
| val snapshot = newServlet(source).getMetricsSnapshot | ||
| val lines = snapshot.linesIterator.toList |
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What changes were proposed in this pull request?
AbstractSource emits a
# HELPand# TYPEline for every metric sample. When a metric family has multiple label sets — like ActiveConnectionCount (per application), RequestSlotsFailedCount (per status code), per-user/app resource consumption, or FlushWorkingQueueSize (per mountpoint) — the same family is exported with repeated# HELPand# TYPElines. This violates the Prometheus exposition format.The fix is to override PrometheusServlet.getMetricsSnapshot to keep only the first
# HELPand# TYPEline per metric family while preserving all sample lines, producing valid Prometheus output.I also added a PrometheusServletSuite covering a multi-label-set counter and a distinct gauge.
Why are the changes needed?
To dedup the help and type lines to no longer violate prometheus exposition format.
Does this PR resolve a correctness bug?
Does this PR introduce any user-facing change?
How was this patch tested?
CI/CD