Usage counter for Top N queries

src/main/java/org/opensearch/plugin/insights/core/metrics/OperationalMetric.java

@@ -18,7 +18,8 @@ public enum OperationalMetric {
     INVALID_INDEX_PATTERN_EXCEPTIONS("Number of invalid index pattern exceptions"),
     DATA_INGEST_EXCEPTIONS("Number of exceptions during data ingest in Query Insights"),
     QUERY_CATEGORIZE_EXCEPTIONS("Number of exceptions when categorizing the queries"),
-    EXPORTER_FAIL_TO_CLOSE_EXCEPTION("Number of failures when closing the exporter");
+    EXPORTER_FAIL_TO_CLOSE_EXCEPTION("Number of failures when closing the exporter"),
+    TOP_N_QUERIES_USAGE_COUNT("Number of times the top n queries API is used");
 
     private final String description;
 

src/main/java/org/opensearch/plugin/insights/core/service/TopQueriesService.java

@@ -53,13 +53,17 @@
 import org.opensearch.plugin.insights.rules.model.SearchQueryRecord;
 import org.opensearch.plugin.insights.rules.model.healthStats.TopQueriesHealthStats;
 import org.opensearch.plugin.insights.settings.QueryInsightsSettings;
+import org.opensearch.telemetry.metrics.tags.Tags;
 import org.opensearch.threadpool.ThreadPool;
 
 /**
  * Service responsible for gathering and storing top N queries
  * with high latency or resource usage
  */
 public class TopQueriesService {
+    private static final String METRIC_TYPE_TAG = "metric_type";
+    private static final String GROUPBY_TAG = "groupby";
+
     /**
      * Logger of the local index exporter
      */
@@ -344,6 +348,13 @@ public void validateExporterAndReaderConfig(Settings settings) {
      */
     public List<SearchQueryRecord> getTopQueriesRecords(final boolean includeLastWindow, final String from, final String to)
         throws IllegalArgumentException {
+        OperationalMetricsCounter.getInstance()
+            .incrementCounter(
+                OperationalMetric.TOP_N_QUERIES_USAGE_COUNT,
+                Tags.create()
+                    .addTag(METRIC_TYPE_TAG, this.metricType.name())
+                    .addTag(GROUPBY_TAG, this.queryGrouper.getGroupingType().name())
+            );
         if (!enabled) {
             throw new IllegalArgumentException(
                 String.format(Locale.ROOT, "Cannot get top n queries for [%s] when it is not enabled.", metricType.toString())

src/test/java/org/opensearch/plugin/insights/core/metrics/OperationalMetricsCounterTests.java

@@ -35,7 +35,7 @@ public void testSingletonInitializationAndIncrement() {
         OperationalMetricsCounter.initialize(CLUSTER_NAME, metricsRegistry);
         OperationalMetricsCounter instance = OperationalMetricsCounter.getInstance();
         ArgumentCaptor<String> nameCaptor = ArgumentCaptor.forClass(String.class);
-        verify(metricsRegistry, times(8)).createCounter(nameCaptor.capture(), any(), eq("1"));
+        verify(metricsRegistry, times(9)).createCounter(nameCaptor.capture(), any(), eq("1"));
         assertNotNull(instance);
         instance.incrementCounter(OperationalMetric.LOCAL_INDEX_READER_PARSING_EXCEPTIONS);
         instance.incrementCounter(OperationalMetric.LOCAL_INDEX_READER_PARSING_EXCEPTIONS);

src/test/java/org/opensearch/plugin/insights/core/service/TopQueriesServiceTests.java

@@ -8,7 +8,9 @@
 
 package org.opensearch.plugin.insights.core.service;
 
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 import java.util.List;
 import java.util.concurrent.TimeUnit;
@@ -17,12 +19,15 @@
 import org.opensearch.common.unit.TimeValue;
 import org.opensearch.plugin.insights.QueryInsightsTestUtils;
 import org.opensearch.plugin.insights.core.exporter.QueryInsightsExporterFactory;
+import org.opensearch.plugin.insights.core.metrics.OperationalMetricsCounter;
 import org.opensearch.plugin.insights.core.reader.QueryInsightsReaderFactory;
 import org.opensearch.plugin.insights.rules.model.GroupingType;
 import org.opensearch.plugin.insights.rules.model.MetricType;
 import org.opensearch.plugin.insights.rules.model.SearchQueryRecord;
 import org.opensearch.plugin.insights.rules.model.healthStats.TopQueriesHealthStats;
 import org.opensearch.plugin.insights.settings.QueryInsightsSettings;
+import org.opensearch.telemetry.metrics.Counter;
+import org.opensearch.telemetry.metrics.MetricsRegistry;
 import org.opensearch.test.OpenSearchTestCase;
 import org.opensearch.threadpool.ThreadPool;
 
@@ -34,13 +39,20 @@ public class TopQueriesServiceTests extends OpenSearchTestCase {
     private final ThreadPool threadPool = mock(ThreadPool.class);
     private final QueryInsightsExporterFactory queryInsightsExporterFactory = mock(QueryInsightsExporterFactory.class);
     private final QueryInsightsReaderFactory queryInsightsReaderFactory = mock(QueryInsightsReaderFactory.class);
+    private MetricsRegistry metricsRegistry;
 
     @Before
     public void setup() {
         topQueriesService = new TopQueriesService(MetricType.LATENCY, threadPool, queryInsightsExporterFactory, queryInsightsReaderFactory);
         topQueriesService.setTopNSize(Integer.MAX_VALUE);
         topQueriesService.setWindowSize(new TimeValue(Long.MAX_VALUE));
         topQueriesService.setEnabled(true);
+
+        metricsRegistry = mock(MetricsRegistry.class);
+        when(metricsRegistry.createCounter(any(String.class), any(String.class), any(String.class))).thenAnswer(
+            invocation -> mock(Counter.class)
+        );
+        OperationalMetricsCounter.initialize("cluster", metricsRegistry);
     }
 
     public void testIngestQueryDataWithLargeWindow() {