fix(common-utils): count distinct attribute values on gauge metric charts

.changeset/gauge-count-distinct-value-expression.md

@@ -0,0 +1,12 @@
+---
+'@hyperdx/common-utils': patch
+'@hyperdx/app': patch
+'@hyperdx/api': patch
+---
+
+fix: count distinct attribute values on gauge metric charts
+
+`count_distinct` on a gauge metric ignored its value expression and counted the
+distinct metric values instead, so counting `Attributes['name']` on an info
+metric returned 1 or 2. It now counts the given expression. The default `Value`
+expression and every other aggregation still use the bucketed metric value.

packages/common-utils/src/__tests__/renderChartConfig.test.ts

@@ -273,6 +273,67 @@ describe('renderChartConfig', () => {
     expect(actual).toMatchSnapshot();
   });
 
+  describe('count_distinct on a gauge metric', () => {
+    const renderGaugeSelect = async (select: {
+      aggFn?: string;
+      valueExpression: string;
+    }) =>
+      parameterizedQueryToSql(
+        await renderChartConfig(
+          {
+            ...gaugeConfiguration,
+            select: [
+              {
+                aggFn: 'count_distinct',
+                metricName: 'argocd_app_info',
+                metricType: MetricsDataType.Gauge,
+                ...select,
+              },
+            ],
+          },
+          mockMetadata,
+          querySettings,
+        ),
+      );
+
+    it('counts the distinct values of an attribute expression', async () => {
+      const sql = await renderGaugeSelect({
+        valueExpression: "Attributes['name']",
+      });
+      expect(sql).toContain("count(DISTINCT Attributes['name'])");
+      expect(sql).not.toContain('count(DISTINCT LastValue)');
+    });
+
+    it('still counts the bucketed metric value for the default Value expression', async () => {
+      const sql = await renderGaugeSelect({ valueExpression: 'Value' });
+      expect(sql).toContain('count(DISTINCT LastValue)');
+    });
+
+    it('still counts the bucketed metric value for an expression over Value', async () => {
+      const sql = await renderGaugeSelect({ valueExpression: 'Value * 100' });
+      expect(sql).toContain('count(DISTINCT LastValue)');
+      expect(sql).not.toContain('Value * 100');
+    });
+
+    it('counts an attribute whose key is Value', async () => {
+      const sql = await renderGaugeSelect({
+        valueExpression: "Attributes['Value']",
+      });
+      expect(sql).toContain("count(DISTINCT Attributes['Value'])");
+    });
+
+    it('keeps other aggregations on the bucketed metric value', async () => {
+      const sql = await renderGaugeSelect({
+        aggFn: 'max',
+        valueExpression: "Attributes['name']",
+      });
+      expect(sql).toMatch(
+        /SELECT max\(\s*toFloat64OrDefault\(toString\(LastValue\)\)/,
+      );
+      expect(sql).not.toContain("Attributes['name']");
+    });
+  });
+
   it('should generate sql for a single sum metric', async () => {
     const config: ChartConfigWithOptDateRange = {
       displayType: DisplayType.Line,

packages/common-utils/src/core/renderChartConfig.ts

@@ -2101,7 +2101,16 @@ async function translateMetricChartConfig(
       select: [
         {
           ..._select,
-          valueExpression: 'LastValue',
+          // count_distinct may count an attribute, which Bucketed still carries;
+          // Bucketed has no Value column, only LastValue
+          valueExpression:
+            _select.aggFn === 'count_distinct' &&
+            _select.valueExpression &&
+            !/\bValue\b/.test(
+              _select.valueExpression.replace(/'(?:[^'\\]|\\.)*'/g, "''"),
+            )
+              ? _select.valueExpression
+              : 'LastValue',
           aggCondition: '', // clear up the condition since the where clause is already applied at the upstream CTE
         },
       ],