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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* 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;
/**
* 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 limitMultiplier;
OptimizeFor(Function limitMultiplier)
{
this.limitMultiplier = limitMultiplier;
}
public int topKFor(int limit)
{
return (int)(limitMultiplier.apply(limit) * limit);
}
public static OptimizeFor fromString(String value)
{
return valueOf(value.toUpperCase());
}
}