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fix(core): Ensure metrics past MAX_METRIC_BUFFER_SIZE are not swallowed #18212

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andreiborza merged 3 commits into from
Nov 17, 2025
Merged

fix(core): Ensure metrics past MAX_METRIC_BUFFER_SIZE are not swallowed #18212

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d1ea9e9
fix(core): Ensure metrics past MAX_METRIC_BUFFER_SIZE are not swallowed
andreiborza Nov 14, 2025
f0737fa
Add test
andreiborza Nov 14, 2025
1a4e02a
Ensure metric that triggers flush on MAX_METRIC_BUFFER_SIZE is not sw…
andreiborza Nov 14, 2025
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5 changes: 4 additions & 1 deletion packages/core/test/lib/metrics/internal.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -256,7 +256,10 @@ describe('_INTERNAL_captureMetric', () => {
// Add one more to trigger flush
_INTERNAL_captureMetric({ type: 'counter', name: 'trigger.flush', value: 999 }, { scope });

expect(_INTERNAL_getMetricBuffer(client)).toEqual([]);
// After flushing the 1000 metrics, the new metric starts a fresh buffer with 1 item
const buffer = _INTERNAL_getMetricBuffer(client);
expect(buffer).toHaveLength(1);
expect(buffer?.[0]?.name).toBe('trigger.flush');
Comment on lines +259 to +262
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@sentry sentry bot Nov 14, 2025

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Bug: A metric that triggers a buffer flush is lost because the flush operation clears the buffer after the new metric has been added but before it's processed.
Severity: CRITICAL | Confidence: 1.00

🔍 Detailed Analysis

The _INTERNAL_captureSerializedMetric function incorrectly handles metrics when the buffer reaches MAX_METRIC_BUFFER_SIZE. When a new metric arrives, it's added to the buffer via bufferMap.set(client, [...metricBuffer, serializedMetric]). However, the subsequent flush condition check if (metricBuffer.length >= MAX_METRIC_BUFFER_SIZE) and the flush operation _INTERNAL_flushMetricsBuffer(client, metricBuffer) use the old metricBuffer reference (before the new metric was added). This leads to the newly added metric being present in the map when _INTERNAL_flushMetricsBuffer is called, but then being lost when _getBufferMap().set(client, []) clears the entire buffer, including the new metric. This results in data loss for metrics that trigger a buffer flush.

💡 Suggested Fix

Modify _INTERNAL_captureSerializedMetric to ensure that the _INTERNAL_flushMetricsBuffer function is called with the updated buffer, or that the new metric is handled correctly after the old buffer is flushed and cleared, perhaps by re-adding it to a newly cleared buffer.

🤖 Prompt for AI Agent 
Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: packages/core/test/lib/metrics/internal.test.ts#L259-L262

Potential issue: The `_INTERNAL_captureSerializedMetric` function incorrectly handles
metrics when the buffer reaches `MAX_METRIC_BUFFER_SIZE`. When a new metric arrives,
it's added to the buffer via `bufferMap.set(client, [...metricBuffer,
serializedMetric])`. However, the subsequent flush condition check `if
(metricBuffer.length >= MAX_METRIC_BUFFER_SIZE)` and the flush operation
`_INTERNAL_flushMetricsBuffer(client, metricBuffer)` use the *old* `metricBuffer`
reference (before the new metric was added). This leads to the newly added metric being
present in the map when `_INTERNAL_flushMetricsBuffer` is called, but then being lost
when `_getBufferMap().set(client, [])` clears the entire buffer, including the new
metric. This results in data loss for metrics that trigger a buffer flush.

Did we get this right? 👍 / 👎 to inform future reviews.

Reference_id: 2692398

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@andreiborza andreiborza Nov 14, 2025

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That's what we are fixing with 1a4e02a

});

it('does not flush metrics buffer when it is empty', () => {
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