From 5a41f0c2b65f2270b19852c009e646fa8ab99a91 Mon Sep 17 00:00:00 2001
From: Deshi Xiao <xiaods@gmail.com>
Date: Sat, 18 Oct 2025 17:05:41 +0800
Subject: [PATCH] Fix metrics disappearing when label schema changes in
 aggregation
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This fixes issue #224 where metrics would disappear from the repo's
aggregated /metrics endpoint after updating metric definitions to add
or remove labels.

**Root Cause:**
In MetricDataSum::sum(), the schema validation (type, shape, dimensions)
was only performed when initial=true. This meant that when a metric's
label structure changed at runtime (e.g., from ['label_one'] to
['label_one', 'label_two']), the shape mismatch was not detected during
regular aggregation cycles.

**The Bug (lines 832-836):**
```cpp
if (!ent || (initial && (
  ent->type != type ||
  ent->shape != shape ||
  ent->dimensions != e->dimensions
))) {
```

When initial=false, schema changes were silently ignored, causing:
- Metrics with new schemas to be aggregated into entries with old schemas
- Mismatched dimensions leading to incorrect aggregation
- Metrics appearing in worker /metrics but missing from repo /metrics

**The Fix:**
Always validate schema consistency, not just during initial aggregation:
```cpp
if (!ent ||
  ent->type != type ||
  ent->shape != shape ||
  ent->dimensions != e->dimensions
) {
```

Now when a metric's schema changes, the entry is properly recreated with
the new schema, ensuring metrics are correctly aggregated and visible in
the repo's /metrics endpoint.

**Testing:**
Reproduced with the test case in issue description:
1. Create metric with one label
2. Update to two labels
3. Verify metric now appears in repo /metrics (previously disappeared)

Note: MetricHistory already had the correct implementation (lines 1117-1120,
1171-1174) and did not require changes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 src/api/stats.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/api/stats.cpp b/src/api/stats.cpp
index 80abc26ae..6c3e0a57d 100644
--- a/src/api/stats.cpp
+++ b/src/api/stats.cpp
@@ -829,11 +829,11 @@ void MetricDataSum::sum(MetricData &data, bool initial) {
     auto *shape = pjs::Str::make(e->shape)->retain();
 
     auto &ent = m_entry_map[name];
-    if (!ent || (initial && (
+    if (!ent ||
       ent->type != type ||
       ent->shape != shape ||
       ent->dimensions != e->dimensions
-    ))) {
+    ) {
       if (!ent) {
         ent = new Entry;
         m_entries.push(ent);