[server] Fix NPE for ServerReadQuotaUsageStats when store has no vers…

…ion or traffic (#1291)

* [server] Fix NPE for ServerReadQuotaUsageStats when store has no version or traffic

1. Prevent NPE in ServerReadQuotaUsageStats's async gauges when a store has no version or traffic.
2. Set backup version using version list in handle store change since the old behavior will not set the correct backup version after server restart.

services/venice-server/src/main/java/com/linkedin/venice/listener/ReadQuotaEnforcementHandler.java

@@ -413,9 +413,12 @@ public void handleStoreChanged(Store store) {
 
     List<String> topics =
         store.getVersions().stream().map((version) -> version.kafkaTopicName()).collect(Collectors.toList());
+    int currentVersion = store.getCurrentVersion();
+    int backupVersion = 0;
     for (String topic: topics) {
       toBeRemovedTopics.remove(topic);
       customizedViewRepository.subscribeRoutingDataChange(topic, this);
+      int versionNumber = Version.parseVersionFromKafkaTopicName(topic);
       try {
         /**
          * make sure we're up-to-date after registering as a listener
@@ -427,8 +430,12 @@ public void handleStoreChanged(Store store) {
          *
          */
         this.onCustomizedViewChange(customizedViewRepository.getPartitionAssignments(topic));
+        if (versionNumber != currentVersion && versionNumber > backupVersion
+            && VersionStatus.isBootstrapCompleted(store.getVersionStatus(versionNumber))) {
+          backupVersion = versionNumber;
+        }
       } catch (VeniceNoHelixResourceException e) {
-        Version version = store.getVersion(Version.parseVersionFromKafkaTopicName(topic));
+        Version version = store.getVersion(versionNumber);
         if (version != null && version.getStatus().equals(VersionStatus.ONLINE)) {
           /**
            * The store metadata believes this version is online, but the partition assignment is not in the
@@ -462,7 +469,12 @@ public void handleStoreChanged(Store store) {
       }
     }
     removeTopics(toBeRemovedTopics);
-    stats.setCurrentVersion(store.getName(), store.getCurrentVersion());
+    if (currentVersion > 0) {
+      stats.setCurrentVersion(store.getName(), currentVersion);
+    }
+    if (backupVersion > 0) {
+      stats.setBackupVersion(store.getName(), backupVersion);
+    }
   }
 
   private Set<String> getStoreTopics(String storeName) {

services/venice-server/src/main/java/com/linkedin/venice/stats/AggServerQuotaUsageStats.java

@@ -37,4 +37,8 @@ public void setNodeQuotaResponsibility(String storeName, int version, long nodeK
   public void setCurrentVersion(String storeName, int version) {
     getStoreStats(storeName).setCurrentVersion(version);
   }
+
+  public void setBackupVersion(String storeName, int version) {
+    getStoreStats(storeName).setBackupVersion(version);
+  }
 }

services/venice-server/src/main/java/com/linkedin/venice/stats/ServerReadQuotaUsageStats.java

@@ -66,15 +66,16 @@ public ServerReadQuotaUsageStats(MetricsRepository metricsRepository, String nam
 
   public void setCurrentVersion(int version) {
     int oldCurrentVersion = currentVersion.get();
-    if (version == oldCurrentVersion) {
+    if (version != oldCurrentVersion) {
       // Defensive coding since set current version can be called multiple times with the same current version
-      return;
+      currentVersion.compareAndSet(oldCurrentVersion, version);
     }
-    if (currentVersion.compareAndSet(oldCurrentVersion, version)) {
-      // Old current version becomes the backup. This should work even if:
-      // a) we rolled back current version
-      // b) current version used to be 0
-      backupVersion.set(oldCurrentVersion);
+  }
+
+  public void setBackupVersion(int version) {
+    int oldBackupVersion = backupVersion.get();
+    if (version != oldBackupVersion) {
+      backupVersion.compareAndSet(oldBackupVersion, version);
     }
   }
 
@@ -114,24 +115,26 @@ private ServerReadQuotaVersionedStats getVersionedStats(int version) {
     return versionedStats.computeIfAbsent(version, (ignored) -> new ServerReadQuotaVersionedStats(time, metricConfig));
   }
 
-  private Double getVersionedRequestedQPS(int version) {
+  // Package private for testing purpose
+  final Double getVersionedRequestedQPS(int version) {
     if (version < 1) {
       return Double.NaN;
     }
-    return versionedStats.get(version).getRequestedQPS();
+    return getVersionedStats(version).getRequestedQPS();
   }
 
-  private Double getVersionedRequestedKPS(int version) {
+  // Package private for testing purpose
+  final Double getVersionedRequestedKPS(int version) {
     if (version < 1) {
       return Double.NaN;
     }
-    return versionedStats.get(version).getRequestedKPS();
+    return getVersionedStats(version).getRequestedKPS();
   }
 
   /**
    * @return the ratio of the read quota usage to the node's quota responsibility
    */
-  private Double getReadQuotaUsageRatio() {
+  final Double getReadQuotaUsageRatio() {
     int version = currentVersion.get();
     if (version < 1 || !versionedStats.containsKey(version)) {
       return Double.NaN;

services/venice-server/src/test/java/com/linkedin/venice/listener/ReadQuotaEnforcementHandlerTest.java

@@ -40,6 +40,7 @@
 import com.linkedin.venice.meta.ReadOnlyStoreRepository;
 import com.linkedin.venice.meta.Store;
 import com.linkedin.venice.meta.Version;
+import com.linkedin.venice.meta.VersionStatus;
 import com.linkedin.venice.protocols.VeniceServerResponse;
 import com.linkedin.venice.read.RequestType;
 import com.linkedin.venice.response.VeniceReadResponseStatus;
@@ -831,6 +832,7 @@ private Store setUpStoreMock(
     doReturn(versionList).when(store).getVersions();
     doReturn(readQuota).when(store).getReadQuotaInCU();
     doReturn(readQuotaEnabled).when(store).isStorageNodeReadQuotaEnabled();
+    doReturn(VersionStatus.ONLINE).when(store).getVersionStatus(anyInt());
     return store;
   }
 

services/venice-server/src/test/java/com/linkedin/venice/stats/AggServerReadQuotaUsageStatsTest.java

@@ -30,7 +30,7 @@ public void testAggServerQuotaUsageStats() {
     String totalReadQuotaRequestedKPSString = ".total--current_quota_request_key_count.Gauge";
     long batchSize = 100;
     long batchSize2 = 200;
-    aggServerQuotaUsageStats.setCurrentVersion(storeName, 1);
+    aggServerQuotaUsageStats.setBackupVersion(storeName, 1);
     aggServerQuotaUsageStats.setCurrentVersion(storeName, 2);
     aggServerQuotaUsageStats.setCurrentVersion(storeName2, 1);
     aggServerQuotaUsageStats.recordAllowed(storeName, 1, batchSize);

services/venice-server/src/test/java/com/linkedin/venice/stats/ServerReadQuotaUsageStatsTest.java

@@ -21,4 +21,33 @@ public void testGetReadQuotaUsageRatio() {
     Assert.assertTrue(
         metricsRepository.getMetric(".test-store--quota_requested_usage_ratio.Gauge").value() <= usageRatio);
   }
+
+  @Test
+  public void testGetReadQuotaMetricsWithNoVersionOrRecordings() {
+    MetricsRepository metricsRepository = new MetricsRepository();
+    String storeName = "test-store";
+    int currentVersion = 3;
+    int backupVersion = 2;
+    ServerReadQuotaUsageStats stats = new ServerReadQuotaUsageStats(metricsRepository, storeName);
+    // Stats shouldn't fail if the store don't have any versions yet
+    Assert.assertEquals(stats.getVersionedRequestedQPS(backupVersion), 0d);
+    Assert.assertEquals(stats.getVersionedRequestedQPS(currentVersion), 0d);
+    Assert.assertEquals(stats.getVersionedRequestedKPS(backupVersion), 0d);
+    Assert.assertEquals(stats.getVersionedRequestedKPS(currentVersion), 0d);
+    Assert.assertEquals(stats.getReadQuotaUsageRatio(), Double.NaN);
+    // Stats shouldn't fail if there are no recordings yet
+    stats.setCurrentVersion(currentVersion);
+    stats.setBackupVersion(backupVersion);
+    Assert.assertEquals(stats.getVersionedRequestedQPS(backupVersion), 0d);
+    Assert.assertEquals(stats.getVersionedRequestedQPS(currentVersion), 0d);
+    Assert.assertEquals(stats.getVersionedRequestedKPS(backupVersion), 0d);
+    Assert.assertEquals(stats.getVersionedRequestedKPS(currentVersion), 0d);
+    Assert.assertEquals(stats.getReadQuotaUsageRatio(), Double.NaN);
+    // The replica receives some assignment and traffic for current version
+    stats.setNodeQuotaResponsibility(currentVersion, 1000);
+    stats.recordAllowed(currentVersion, 100);
+    Assert.assertTrue(stats.getReadQuotaUsageRatio() > 0);
+    Assert.assertTrue(stats.getVersionedRequestedQPS(currentVersion) > 0);
+    Assert.assertTrue(stats.getVersionedRequestedKPS(currentVersion) > 0);
+  }
 }