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.

1 files changed, 2 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