Add query control of top-k-probability.

4 files changed, 34 insertions, 7 deletions

diff --git a/container-search/src/main/java/com/yahoo/search/dispatch/Dispatcher.java b/container-search/src/main/java/com/yahoo/search/dispatch/Dispatcher.java
index 9c46d194fb3..3c26612e8e1 100644
--- a/container-search/src/main/java/com/yahoo/search/dispatch/Dispatcher.java
+++ b/container-search/src/main/java/com/yahoo/search/dispatch/Dispatcher.java
@@ -50,6 +50,7 @@ public class Dispatcher extends AbstractComponent {
     public static final String DISPATCH = "dispatch";
     private static final String INTERNAL = "internal";
     private static final String PROTOBUF = "protobuf";
+    private static final String TOP_K_PROBABILITY = "top-k-probability";
 
     private static final String INTERNAL_METRIC = "dispatch_internal";
 
@@ -58,6 +59,9 @@ public class Dispatcher extends AbstractComponent {
     /** If enabled, search queries will use protobuf rpc */
     public static final CompoundName dispatchProtobuf = CompoundName.fromComponents(DISPATCH, PROTOBUF);
 
+    /** If set will control computation of how many hits will be fetched from each partition.*/
+    public static final CompoundName topKProbability = CompoundName.fromComponents(DISPATCH, TOP_K_PROBABILITY);
+
     /** A model of the search cluster this dispatches to */
     private final SearchCluster searchCluster;
     private final ClusterMonitor clusterMonitor;
@@ -79,6 +83,7 @@ public class Dispatcher extends AbstractComponent {
         argumentType.setBuiltin(true);
         argumentType.addField(new FieldDescription(INTERNAL, FieldType.booleanType));
         argumentType.addField(new FieldDescription(PROTOBUF, FieldType.booleanType));
+        argumentType.addField(new FieldDescription(TOP_K_PROBABILITY, FieldType.doubleType));
         argumentType.freeze();
     }
 
diff --git a/container-search/src/main/java/com/yahoo/search/dispatch/InterleavedSearchInvoker.java b/container-search/src/main/java/com/yahoo/search/dispatch/InterleavedSearchInvoker.java
index bae1eb03e5f..e62848a7f9e 100644
--- a/container-search/src/main/java/com/yahoo/search/dispatch/InterleavedSearchInvoker.java
+++ b/container-search/src/main/java/com/yahoo/search/dispatch/InterleavedSearchInvoker.java
@@ -81,7 +81,12 @@ public class InterleavedSearchInvoker extends SearchInvoker implements ResponseM
 
         int originalHits = query.getHits();
         int originalOffset = query.getOffset();
-        query.setHits(searchCluster.estimateHitsToFetch(query.getHits() + query.getOffset(), invokers.size()));
+        int neededHits = originalHits + originalOffset;
+        Double topkProbabilityOverrride = query.properties().getDouble(Dispatcher.topKProbability);
+        int q = (topkProbabilityOverrride != null)
+                ? searchCluster.estimateHitsToFetch(neededHits, invokers.size(), topkProbabilityOverrride)
+                : searchCluster.estimateHitsToFetch(neededHits, invokers.size());
+        query.setHits(q);
         query.setOffset(0);
 
         for (SearchInvoker invoker : invokers) {
@@ -321,4 +326,7 @@ public class InterleavedSearchInvoker extends SearchInvoker implements ResponseM
     protected LinkedBlockingQueue<SearchInvoker> newQueue() {
         return new LinkedBlockingQueue<>();
     }
+
+    // For testing
+    Collection<SearchInvoker> invokers() { return invokers; }
 }
diff --git a/container-search/src/main/java/com/yahoo/search/dispatch/TopKEstimator.java b/container-search/src/main/java/com/yahoo/search/dispatch/TopKEstimator.java
index 374f919e2bb..2a84481fdf3 100644
--- a/container-search/src/main/java/com/yahoo/search/dispatch/TopKEstimator.java
+++ b/container-search/src/main/java/com/yahoo/search/dispatch/TopKEstimator.java
@@ -9,22 +9,33 @@ import org.apache.commons.math3.distribution.TDistribution;
  */
 public class TopKEstimator {
     private final TDistribution studentT;
-    private final double p;
+    private final double defaultP;
     private final boolean estimate;
 
-    public TopKEstimator(double freedom, double wantedprobability) {
+    private static boolean needEstimate(double p) {
+        return (0.0 < p) && (p < 1.0);
+    }
+    public TopKEstimator(double freedom, double defaultProbability) {
         this.studentT = new TDistribution(null, freedom);
-        p = wantedprobability;
-        estimate = (0.0 < p) && (p < 1.0);
+        defaultP = defaultProbability;
+        estimate = needEstimate(defaultP);
     }
-    double estimateExactK(double k, double n) {
+    double estimateExactK(double k, double n, double p) {
         double variance = k * 1/n * (1 - 1/n);
         double p_inverse = 1 - (1 - p)/n;
         return k/n + studentT.inverseCumulativeProbability(p_inverse) * Math.sqrt(variance);
     }
+    double estimateExactK(double k, double n) {
+        return estimateExactK(k, n, defaultP);
+    }
     public int estimateK(int k, int n) {
         return (estimate && n > 1)
-                ? (int)Math.ceil(estimateExactK(k, n))
+                ? (int)Math.ceil(estimateExactK(k, n, defaultP))
+                : k;
+    }
+    public int estimateK(int k, int n, double p) {
+        return (needEstimate(p) && (n > 1))
+                ? (int)Math.ceil(estimateExactK(k, n, p))
                 : k;
     }
 }
diff --git a/container-search/src/main/java/com/yahoo/search/dispatch/searchcluster/SearchCluster.java b/container-search/src/main/java/com/yahoo/search/dispatch/searchcluster/SearchCluster.java
index 5acafb9e0a5..f31fd666ae9 100644
--- a/container-search/src/main/java/com/yahoo/search/dispatch/searchcluster/SearchCluster.java
+++ b/container-search/src/main/java/com/yahoo/search/dispatch/searchcluster/SearchCluster.java
@@ -246,6 +246,9 @@ public class SearchCluster implements NodeManager<Node> {
     public int estimateHitsToFetch(int wantedHits, int numPartitions) {
         return hitEstimator.estimateK(wantedHits, numPartitions);
     }
+    public int estimateHitsToFetch(int wantedHits, int numPartitions, double topKProbability) {
+        return hitEstimator.estimateK(wantedHits, numPartitions, topKProbability);
+    }
 
     public boolean hasInformationAboutAllNodes() {
         return nodesByHost.values().stream().allMatch(node -> node.isWorking() != null);