content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.cassandra.index.sai.disk.v1.vector;
  
  import java.util.function.Function;
  
  import static java.lang.Math.pow;
  import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
  
  /**
   * Allows the vector index searches to be optimised for latency or recall. This is used by the
   * {@link org.apache.cassandra.index.sai.disk.v1.segment.VectorIndexSegmentSearcher} to determine how many results to ask the graph
   * to search for. If we are optimising for {@link #RECALL} we ask for more than the requested limit which
   * (since it will search deeper in the graph) will tend to surface slightly better results.
   */
  public enum OptimizeFor
  {
      LATENCY(limit -> 0.979 + 4.021 * pow(limit, -0.761)), // f(1) =  5.0, f(100) = 1.1, f(1000) = 1.0
      RECALL(limit -> 0.509 + 9.491 * pow(limit, -0.402));  // f(1) = 10.0, f(100) = 2.0, f(1000) = 1.1
  
      private final Function<Integer, Double> limitMultiplier;
  
      OptimizeFor(Function<Integer, Double> limitMultiplier)
      {
          this.limitMultiplier = limitMultiplier;
      }
  
      public int topKFor(int limit)
      {
          return (int)(limitMultiplier.apply(limit) * limit);
      }
  
      public static OptimizeFor fromString(String value)
      {
          return valueOf(toUpperCaseLocalized(value));
      }
  }
  