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, 9 insertions, 0 deletions

diff --git a/config-model/src/main/java/com/yahoo/schema/parser/ConvertParsedRanking.java b/config-model/src/main/java/com/yahoo/schema/parser/ConvertParsedRanking.java
index bdecf6332a0..c25d393c8bf 100644
--- a/config-model/src/main/java/com/yahoo/schema/parser/ConvertParsedRanking.java
+++ b/config-model/src/main/java/com/yahoo/schema/parser/ConvertParsedRanking.java
@@ -65,6 +65,8 @@ public class ConvertParsedRanking {
                 (value -> profile.setPostFilterThreshold(value));
         parsed.getApproximateThreshold().ifPresent
                 (value -> profile.setApproximateThreshold(value));
+        parsed.getTargetHitsMaxAdjustmentFactor().ifPresent
+                (value -> profile.setTargetHitsMaxAdjustmentFactor(value));
         parsed.getKeepRankCount().ifPresent
             (value -> profile.setKeepRankCount(value));
         parsed.getMinHitsPerThread().ifPresent
diff --git a/config-model/src/main/java/com/yahoo/schema/parser/ParsedRankProfile.java b/config-model/src/main/java/com/yahoo/schema/parser/ParsedRankProfile.java
index 2809ee0c633..1d06b993cdc 100644
--- a/config-model/src/main/java/com/yahoo/schema/parser/ParsedRankProfile.java
+++ b/config-model/src/main/java/com/yahoo/schema/parser/ParsedRankProfile.java
@@ -29,6 +29,7 @@ class ParsedRankProfile extends ParsedBlock {
     private Double termwiseLimit = null;
     private Double postFilterThreshold = null;
     private Double approximateThreshold = null;
+    private Double targetHitsMaxAdjustmentFactor = null;
     private final List<FeatureList> matchFeatures = new ArrayList<>();
     private final List<FeatureList> rankFeatures = new ArrayList<>();
     private final List<FeatureList> summaryFeatures = new ArrayList<>();
@@ -65,6 +66,7 @@ class ParsedRankProfile extends ParsedBlock {
     Optional<Double> getTermwiseLimit() { return Optional.ofNullable(this.termwiseLimit); }
     Optional<Double> getPostFilterThreshold() { return Optional.ofNullable(this.postFilterThreshold); }
     Optional<Double> getApproximateThreshold() { return Optional.ofNullable(this.approximateThreshold); }
+    Optional<Double> getTargetHitsMaxAdjustmentFactor() { return Optional.ofNullable(this.targetHitsMaxAdjustmentFactor); }
     List<FeatureList> getMatchFeatures() { return List.copyOf(this.matchFeatures); }
     List<FeatureList> getRankFeatures() { return List.copyOf(this.rankFeatures); }
     List<FeatureList> getSummaryFeatures() { return List.copyOf(this.summaryFeatures); }
@@ -231,4 +233,9 @@ class ParsedRankProfile extends ParsedBlock {
         this.approximateThreshold = threshold;
     }
 
+    void setTargetHitsMaxAdjustmentFactor(double factor) {
+        verifyThat(targetHitsMaxAdjustmentFactor == null, "already has target-hits-max-adjustment-factor");
+        this.targetHitsMaxAdjustmentFactor = factor;
+    }
+
 }