feat: add persistent query saturation metric

ksqldb-engine/src/main/java/io/confluent/ksql/internal/JmxDataPointsReporter.java

@@ -0,0 +1,98 @@
+/*
+ * Copyright 2021 Confluent Inc.
+ *
+ * Licensed under the Confluent Community License (the "License"); you may not use
+ * this file except in compliance with the License.  You may obtain a copy of the
+ * License at
+ *
+ * http://www.confluent.io/confluent-community-license
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OF ANY KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+
+package io.confluent.ksql.internal;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.kafka.common.MetricName;
+import org.apache.kafka.common.metrics.Gauge;
+import org.apache.kafka.common.metrics.MetricConfig;
+import org.apache.kafka.common.metrics.Metrics;
+
+public class JmxDataPointsReporter implements MetricsReporter {
+  private final Metrics metrics;
+  private final String group;
+  private final Map<MetricName, DataPointBasedGauge> gauges = new ConcurrentHashMap<>();
+  private final Duration staleThreshold;
+
+  public JmxDataPointsReporter(
+      final Metrics metrics,
+      final String group,
+      final Duration staleThreshold
+  ) {
+    this.metrics = Objects.requireNonNull(metrics, "metrics");
+    this.group = Objects.requireNonNull(group, "group");
+    this.staleThreshold = Objects.requireNonNull(staleThreshold, "staleThreshold");
+  }
+
+  @Override
+  public void report(final List<DataPoint> dataPoints) {
+    dataPoints.forEach(this::report);
+  }
+
+  private void report(final DataPoint dataPoint) {
+    final MetricName metricName
+        = metrics.metricName(dataPoint.getName(), group, dataPoint.getTags());
+    if (gauges.containsKey(metricName)) {
+      gauges.get(metricName).dataPointRef.set(dataPoint);
+    } else {
+      gauges.put(metricName, new DataPointBasedGauge(dataPoint, staleThreshold));
+      metrics.addMetric(metricName, gauges.get(metricName));
+    }
+  }
+
+  @Override
+  public void cleanup(final String name, final Map<String, String> tags) {
+    final MetricName metricName = metrics.metricName(name, group, tags);
+    metrics.removeMetric(metricName);
+    gauges.remove(metricName);
+  }
+
+  @Override
+  public void close() {
+  }
+
+  @Override
+  public void configure(final Map<String, ?> map) {
+  }
+
+  private static final class DataPointBasedGauge implements Gauge<Object> {
+    private final AtomicReference<DataPoint> dataPointRef;
+    private final Duration staleThreshold;
+
+    private DataPointBasedGauge(
+        final DataPoint initial,
+        final Duration staleThreshold
+    ) {
+      this.dataPointRef = new AtomicReference<>(initial);
+      this.staleThreshold = staleThreshold;
+    }
+
+    @Override
+    public Object value(final MetricConfig metricConfig, final long now) {
+      final DataPoint dataPoint = dataPointRef.get();
+      if (dataPoint.getTime().isAfter(Instant.ofEpochMilli(now).minus(staleThreshold))) {
+        return dataPoint.getValue();
+      }
+      return null;
+    }
+  }
+}

ksqldb-engine/src/main/java/io/confluent/ksql/internal/MetricsReporter.java

@@ -24,7 +24,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.function.Supplier;
 
 /**
  * This interface is used to report metrics as data points to a
@@ -107,7 +106,12 @@ public int hashCode() {
   /**
    * Reports a list of data points.
    *
-   * @param dataPointSupplier supplier of the list of data points
+   * @param dataPoints the list of data points
    */
-  void report(Supplier<List<DataPoint>> dataPointSupplier);
-}
+  void report(List<DataPoint> dataPoints);
+
+  /**
+   * Notifies the reporter that the metric with name and tags can be cleaned up
+   */
+  void cleanup(String name, Map<String, String> tags);
+}

ksqldb-engine/src/main/java/io/confluent/ksql/util/QueryMetadataImpl.java

@@ -73,9 +73,9 @@ public class QueryMetadataImpl implements QueryMetadata {
 
   private volatile boolean everStarted = false;
   protected volatile boolean closed = false;
+  private volatile KafkaStreams kafkaStreams;
   // These fields don't need synchronization because they are initialized in initialize() before
   // the object is made available to other threads.
-  private KafkaStreams kafkaStreams;
   private boolean initialized = false;
   private boolean corruptionCommandTopic = false;