fix(metrics): flush metrics when data points array reaches max size (#1548)

* test: added failing test

* fix(metrics): flush metrics when values array reaches max size

Author: dreamorosi

Diff for: packages/metrics/src/Metrics.ts

@@ -7,6 +7,7 @@ import {
   MAX_METRICS_SIZE,
   DEFAULT_NAMESPACE,
   COLD_START_METRIC,
+  MAX_METRIC_VALUES_SIZE,
 } from './constants';
 import {
   MetricsOptions,
@@ -662,7 +663,10 @@ class Metrics extends Utility implements MetricsInterface {
   }
 
   /**
-   * Stores a metric in the buffer
+   * Stores a metric in the buffer.
+   *
+   * If the buffer is full, or the metric reaches the maximum number of values,
+   * the buffer is published to stdout.
    *
    * @param name The name of the metric to store
    * @param unit The unit of the metric to store
@@ -692,6 +696,9 @@ class Metrics extends Utility implements MetricsInterface {
         storedMetric.value = [storedMetric.value];
       }
       storedMetric.value.push(value);
+      if (storedMetric.value.length === MAX_METRIC_VALUES_SIZE) {
+        this.publishStoredMetrics();
+      }
     }
   }
 }

Diff for: packages/metrics/src/constants.ts

@@ -1,4 +1,13 @@
-export const COLD_START_METRIC = 'ColdStart';
-export const DEFAULT_NAMESPACE = 'default_namespace';
-export const MAX_METRICS_SIZE = 100;
-export const MAX_DIMENSION_COUNT = 29;
+const COLD_START_METRIC = 'ColdStart';
+const DEFAULT_NAMESPACE = 'default_namespace';
+const MAX_METRICS_SIZE = 100;
+const MAX_METRIC_VALUES_SIZE = 100;
+const MAX_DIMENSION_COUNT = 29;
+
+export {
+  COLD_START_METRIC,
+  DEFAULT_NAMESPACE,
+  MAX_METRICS_SIZE,
+  MAX_METRIC_VALUES_SIZE,
+  MAX_DIMENSION_COUNT,
+};

Diff for: packages/metrics/tests/unit/Metrics.test.ts

@@ -16,6 +16,7 @@ import {
   DEFAULT_NAMESPACE,
   MAX_DIMENSION_COUNT,
   MAX_METRICS_SIZE,
+  MAX_METRIC_VALUES_SIZE,
 } from '../../src/constants';
 import { setupDecoratorLambdaHandler } from '../helpers/metricsUtils';
 import {
@@ -701,6 +702,34 @@ describe('Class: Metrics', () => {
       );
     });
 
+    test('it should publish metrics when the array of values reaches the maximum size', () => {
+      // Prepare
+      const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });
+      const consoleSpy = jest.spyOn(console, 'log');
+      const metricName = 'test-metric';
+
+      // Act
+      for (let i = 0; i <= MAX_METRIC_VALUES_SIZE; i++) {
+        metrics.addMetric(`${metricName}`, MetricUnits.Count, i);
+      }
+      metrics.publishStoredMetrics();
+
+      // Assess
+      // 2 calls to console.log: 1 for the first batch of metrics, 1 for the second batch (explicit call)
+      expect(consoleSpy).toHaveBeenCalledTimes(2);
+      const firstMetricsJson = JSON.parse(
+        consoleSpy.mock.calls[0][0]
+      ) as EmfOutput;
+      const secondMetricsJson = JSON.parse(
+        consoleSpy.mock.calls[1][0]
+      ) as EmfOutput;
+
+      // The first batch of values should be an array of size MAX_METRIC_VALUES_SIZE
+      expect(firstMetricsJson[metricName]).toHaveLength(MAX_METRIC_VALUES_SIZE);
+      // The second should be a single value (the last value added, which is 100 given we start from 0)
+      expect(secondMetricsJson[metricName]).toEqual(100);
+    });
+
     test('it should not publish metrics if stored metrics count has not reached max metric size threshold', () => {
       // Prepare
       const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });