Add bidder cardinality metric

docs/metrics.md

@@ -23,6 +23,7 @@ Other available metrics can found at [Vert.x Dropwizard Metrics](https://vertx.i
 - `imps_native` - number of native impressions
 - `imps_audio` - number of audio impressions
 - `requests.(ok|badinput|err|networkerr|blacklisted_account|blacklisted_app).(openrtb2-web|openrtb-app|amp|legacy)` - number of requests broken down by status and type
+- `bidder-cardinality.<cardinality>.requests` - number of requests targeting `<cardinality>` of bidders
 - `connection_accept_errors` - number of errors occurred while establishing HTTP connection
 - `db_circuitbreaker_opened` - number of times database circuit breaker was opened (database is unavailable)
 - `db_circuitbreaker_closed` - number of times database circuit breaker was closed (database is available again)

src/main/java/org/prebid/server/auction/ExchangeService.java

@@ -780,9 +780,13 @@ private ExtRequest prepareExt(String bidder,
     /**
      * Updates 'account.*.request', 'request' and 'no_cookie_requests' metrics for each {@link BidderRequest}.
      */
-    private List<BidderRequest> updateRequestMetric(List<BidderRequest> bidderRequests, UidsCookie uidsCookie,
-                                                    BidderAliases aliases, String publisherId,
+    private List<BidderRequest> updateRequestMetric(List<BidderRequest> bidderRequests,
+                                                    UidsCookie uidsCookie,
+                                                    BidderAliases aliases,
+                                                    String publisherId,
                                                     MetricName requestTypeMetric) {
+
+        metrics.updateRequestBidderCardinalityMetric(bidderRequests.size());
         metrics.updateAccountRequestMetrics(publisherId, requestTypeMetric);
 
         for (BidderRequest bidderRequest : bidderRequests) {
@@ -793,6 +797,7 @@ private List<BidderRequest> updateRequestMetric(List<BidderRequest> bidderReques
 
             metrics.updateAdapterRequestTypeAndNoCookieMetrics(bidder, requestTypeMetric, !isApp && noBuyerId);
         }
+
         return bidderRequests;
     }
 

src/main/java/org/prebid/server/metric/BidderCardinalityMetrics.java

@@ -0,0 +1,17 @@
+package org.prebid.server.metric;
+
+import com.codahale.metrics.MetricRegistry;
+
+import java.util.Objects;
+import java.util.function.Function;
+
+public class BidderCardinalityMetrics extends UpdatableMetrics {
+
+    BidderCardinalityMetrics(MetricRegistry metricRegistry, CounterType counterType, Integer cardinality) {
+        super(metricRegistry, counterType, nameCreator(Objects.requireNonNull(cardinality)));
+    }
+
+    private static Function<MetricName, String> nameCreator(Integer cardinality) {
+        return metricName -> String.format("bidder-cardinality.%d.%s", cardinality, metricName.toString());
+    }
+}

src/main/java/org/prebid/server/metric/Metrics.java

@@ -28,13 +28,15 @@ public class Metrics extends UpdatableMetrics {
     private final Function<MetricName, RequestStatusMetrics> requestMetricsCreator;
     private final Function<String, AccountMetrics> accountMetricsCreator;
     private final Function<String, AdapterMetrics> adapterMetricsCreator;
+    private final Function<Integer, BidderCardinalityMetrics> bidderCardinalityMetricsCreator;
     private final Function<String, CircuitBreakerMetrics> circuitBreakerMetricsCreator;
     // not thread-safe maps are intentionally used here because it's harmless in this particular case - eventually
     // this all boils down to metrics lookup by underlying metric registry and that operation is guaranteed to be
     // thread-safe
     private final Map<MetricName, RequestStatusMetrics> requestMetrics;
     private final Map<String, AccountMetrics> accountMetrics;
     private final Map<String, AdapterMetrics> adapterMetrics;
+    private final Map<Integer, BidderCardinalityMetrics> bidderCardinailtyMetrics;
     private final UserSyncMetrics userSyncMetrics;
     private final CookieSyncMetrics cookieSyncMetrics;
     private final PrivacyMetrics privacyMetrics;
@@ -51,10 +53,13 @@ public Metrics(MetricRegistry metricRegistry, CounterType counterType, AccountMe
         requestMetricsCreator = requestType -> new RequestStatusMetrics(metricRegistry, counterType, requestType);
         accountMetricsCreator = account -> new AccountMetrics(metricRegistry, counterType, account);
         adapterMetricsCreator = adapterType -> new AdapterMetrics(metricRegistry, counterType, adapterType);
+        bidderCardinalityMetricsCreator = cardinality -> new BidderCardinalityMetrics(
+                metricRegistry, counterType, cardinality);
         circuitBreakerMetricsCreator = id -> new CircuitBreakerMetrics(metricRegistry, counterType, id);
         requestMetrics = new EnumMap<>(MetricName.class);
         accountMetrics = new HashMap<>();
         adapterMetrics = new HashMap<>();
+        bidderCardinailtyMetrics = new HashMap<>();
         userSyncMetrics = new UserSyncMetrics(metricRegistry, counterType);
         cookieSyncMetrics = new CookieSyncMetrics(metricRegistry, counterType);
         privacyMetrics = new PrivacyMetrics(metricRegistry, counterType);
@@ -66,6 +71,10 @@ RequestStatusMetrics forRequestType(MetricName requestType) {
         return requestMetrics.computeIfAbsent(requestType, requestMetricsCreator);
     }
 
+    BidderCardinalityMetrics forBidderCardinality(int cardinality) {
+        return bidderCardinailtyMetrics.computeIfAbsent(cardinality, bidderCardinalityMetricsCreator);
+    }
+
     AccountMetrics forAccount(String account) {
         return accountMetrics.computeIfAbsent(account, accountMetricsCreator);
     }
@@ -172,6 +181,10 @@ public void updateRequestTypeMetric(MetricName requestType, MetricName requestSt
         forRequestType(requestType).incCounter(requestStatus);
     }
 
+    public void updateRequestBidderCardinalityMetric(int bidderCardinality) {
+        forBidderCardinality(bidderCardinality).incCounter(MetricName.requests);
+    }
+
     public void updateAccountRequestMetrics(String accountId, MetricName requestType) {
         final AccountMetricsVerbosityLevel verbosityLevel = accountMetricsVerbosity.forAccount(accountId);
         if (verbosityLevel.isAtLeast(AccountMetricsVerbosityLevel.basic)) {

src/test/java/org/prebid/server/auction/ExchangeServiceTest.java

@@ -2107,6 +2107,7 @@ public void shouldIncrementCommonMetrics() {
         exchangeService.holdAuction(givenRequestContext(bidRequest));
 
         // then
+        verify(metrics).updateRequestBidderCardinalityMetric(1);
         verify(metrics).updateAccountRequestMetrics(eq("accountId"), eq(MetricName.openrtb2web));
         verify(metrics)
                 .updateAdapterRequestTypeAndNoCookieMetrics(eq("someBidder"), eq(MetricName.openrtb2web), eq(true));

src/test/java/org/prebid/server/metric/MetricsTest.java

@@ -449,6 +449,15 @@ public void updateRequestTypeMetricShouldIncrementMetric() {
         assertThat(metricRegistry.counter("requests.networkerr.amp").getCount()).isEqualTo(1);
     }
 
+    @Test
+    public void uupdateRequestBidderCardinalityMetricShouldIncrementMetrics() {
+        // when
+        metrics.updateRequestBidderCardinalityMetric(3);
+
+        // then
+        assertThat(metricRegistry.counter("bidder-cardinality.3.requests").getCount()).isEqualTo(1);
+    }
+
     @Test
     public void updateAccountRequestMetricsShouldIncrementMetrics() {
         // when