Control the auto-adjustment of targetHits in ANN using post-filtering.

When searching the HNSW index in a post-filtering case,
targetHits is auto-adjusted in an effort to still expose targetHits hits to first-phase ranking after post-filtering.
The following formula is now used to ensure an upper bound of adjustedTargetHits,
avoiding that the search in the HNSW index takes too long.

adjustedTargetHits = min(targetHits / estimatedHitRatio, targetHits * targetHitsMaxAdjustmentFactor).

The target-hits-max-adjustment-factor can be set in a rank profile and overriden per query.
The value is in the range [1.0,inf], with the default being 20.0.

When setting this to 1.0, auto-adjustment of targetHits is effectively disabled.

2 files changed, 15 insertions, 2 deletions

diff --git a/container-search/src/main/java/com/yahoo/search/query/properties/QueryProperties.java b/container-search/src/main/java/com/yahoo/search/query/properties/QueryProperties.java
index 800b3a1ba89..99d6959441a 100644
--- a/container-search/src/main/java/com/yahoo/search/query/properties/QueryProperties.java
+++ b/container-search/src/main/java/com/yahoo/search/query/properties/QueryProperties.java
@@ -91,6 +91,7 @@ public class QueryProperties extends Properties {
         addDualCasedRM(map, Matching.MINHITSPERTHREAD, GetterSetter.of(query -> query.getRanking().getMatching().getMinHitsPerThread(), (query, value) -> query.getRanking().getMatching().setMinHitsPerThread(asInteger(value, 0))));
         addDualCasedRM(map, Matching.POST_FILTER_THRESHOLD, GetterSetter.of(query -> query.getRanking().getMatching().getPostFilterThreshold(), (query, value) -> query.getRanking().getMatching().setPostFilterThreshold(asDouble(value, 1.0))));
         addDualCasedRM(map, Matching.APPROXIMATE_THRESHOLD, GetterSetter.of(query -> query.getRanking().getMatching().getApproximateThreshold(), (query, value) -> query.getRanking().getMatching().setApproximateThreshold(asDouble(value, 0.05))));
+        addDualCasedRM(map, Matching.TARGET_HITS_MAX_ADJUSTMENT_FACTOR, GetterSetter.of(query -> query.getRanking().getMatching().getTargetHitsMaxAdjustmentFactor(), (query, value) -> query.getRanking().getMatching().setTargetHitsMaxAdjustmentFactor(asDouble(value, 20.0))));
 
         map.put(CompoundName.fromComponents(Ranking.RANKING, Ranking.MATCH_PHASE, MatchPhase.ATTRIBUTE), GetterSetter.of(query -> query.getRanking().getMatchPhase().getAttribute(), (query, value) -> query.getRanking().getMatchPhase().setAttribute(asString(value, null))));
         map.put(CompoundName.fromComponents(Ranking.RANKING, Ranking.MATCH_PHASE, MatchPhase.ASCENDING), GetterSetter.of(query -> query.getRanking().getMatchPhase().getAscending(), (query, value) -> query.getRanking().getMatchPhase().setAscending(asBoolean(value, false))));
diff --git a/container-search/src/main/java/com/yahoo/search/query/ranking/Matching.java b/container-search/src/main/java/com/yahoo/search/query/ranking/Matching.java
index 35fbd52f967..4d21f32d16d 100644
--- a/container-search/src/main/java/com/yahoo/search/query/ranking/Matching.java
+++ b/container-search/src/main/java/com/yahoo/search/query/ranking/Matching.java
@@ -24,6 +24,7 @@ public class Matching implements Cloneable {
     public static final String MINHITSPERTHREAD = "minHitsPerThread";
     public static final String POST_FILTER_THRESHOLD = "postFilterThreshold";
     public static final String APPROXIMATE_THRESHOLD = "approximateThreshold";
+    public static final String TARGET_HITS_MAX_ADJUSTMENT_FACTOR = "targetHitsMaxAdjustmentFactor";
 
     static {
         argumentType =new QueryProfileType(Ranking.MATCHING);
@@ -35,6 +36,7 @@ public class Matching implements Cloneable {
         argumentType.addField(new FieldDescription(MINHITSPERTHREAD, "integer"));
         argumentType.addField(new FieldDescription(POST_FILTER_THRESHOLD, "double"));
         argumentType.addField(new FieldDescription(APPROXIMATE_THRESHOLD, "double"));
+        argumentType.addField(new FieldDescription(TARGET_HITS_MAX_ADJUSTMENT_FACTOR, "double"));
         argumentType.freeze();
     }
 
@@ -46,6 +48,7 @@ public class Matching implements Cloneable {
     private Integer minHitsPerThread = null;
     private Double postFilterThreshold = null;
     private Double approximateThreshold = null;
+    private Double targetHitsMaxAdjustmentFactor = null;
 
     public Double getTermwiseLimit() { return termwiseLimit; }
     public Integer getNumThreadsPerSearch() { return numThreadsPerSearch; }
@@ -53,6 +56,7 @@ public class Matching implements Cloneable {
     public Integer getMinHitsPerThread() { return minHitsPerThread; }
     public Double getPostFilterThreshold() { return postFilterThreshold; }
     public Double getApproximateThreshold() { return approximateThreshold; }
+    public Double getTargetHitsMaxAdjustmentFactor() { return targetHitsMaxAdjustmentFactor; }
 
     public void setTermwiselimit(double value) {
         if ((value < 0.0) || (value > 1.0)) {
@@ -75,6 +79,9 @@ public class Matching implements Cloneable {
     public void setApproximateThreshold(double threshold) {
         approximateThreshold = threshold;
     }
+    public void setTargetHitsMaxAdjustmentFactor(double factor) {
+        targetHitsMaxAdjustmentFactor = factor;
+    }
 
     /** Internal operation - DO NOT USE */
     public void prepare(RankProperties rankProperties) {
@@ -97,6 +104,9 @@ public class Matching implements Cloneable {
         if (approximateThreshold != null) {
             rankProperties.put("vespa.matching.global_filter.lower_limit", String.valueOf(approximateThreshold));
         }
+        if (targetHitsMaxAdjustmentFactor != null) {
+            rankProperties.put("vespa.matching.nns.target_hits_max_adjustment_factor", String.valueOf(targetHitsMaxAdjustmentFactor));
+        }
     }
 
     @Override
@@ -119,12 +129,14 @@ public class Matching implements Cloneable {
                 Objects.equals(numSearchPartitions, matching.numSearchPartitions) &&
                 Objects.equals(minHitsPerThread, matching.minHitsPerThread) &&
                 Objects.equals(postFilterThreshold, matching.postFilterThreshold) &&
-                Objects.equals(approximateThreshold, matching.approximateThreshold);
+                Objects.equals(approximateThreshold, matching.approximateThreshold) &&
+                Objects.equals(targetHitsMaxAdjustmentFactor, matching.targetHitsMaxAdjustmentFactor);
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(termwiseLimit, numThreadsPerSearch, numSearchPartitions, minHitsPerThread, postFilterThreshold, approximateThreshold);
+        return Objects.hash(termwiseLimit, numThreadsPerSearch, numSearchPartitions, minHitsPerThread,
+                postFilterThreshold, approximateThreshold, targetHitsMaxAdjustmentFactor);
     }
 }