Remove Lucene's PackedInt dependency from Cuckoo filter

qa/mixed-cluster/src/test/java/org/elasticsearch/backwards/RareTermsIT.java

@@ -0,0 +1,86 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.backwards;
+
+import org.elasticsearch.Version;
+import org.elasticsearch.client.Request;
+import org.elasticsearch.client.Response;
+import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.support.XContentMapValues;
+import org.elasticsearch.test.rest.ESRestTestCase;
+import org.hamcrest.Matchers;
+
+import java.io.IOException;
+import java.util.List;
+
+/**
+ * Test that index enough data to trigger the creation of Cuckoo filters.
+ */
+public class RareTermsIT extends ESRestTestCase {
+
+    private static final String index = "idx";
+
+    private void setupMaxBuckets() throws Exception {
+        // increases the max bucket limit for this test
+        final Request request = new Request("PUT", "_cluster/settings");
+        request.setJsonEntity("{ \"transient\" : { \"search.max_buckets\" : 65356 } }");
+        assertOK(client().performRequest(request));
+    }
+
+    private int indexDocs(int numDocs, int id) throws Exception {
+        final Request request = new Request("POST", "/_bulk");
+        final StringBuilder builder = new StringBuilder();
+        for (int i = 0; i < numDocs; ++i) {
+            builder.append("{ \"index\" : { \"_index\" : \"" + index + "\", \"_id\": \"" + id++ + "\" } }\n");
+            builder.append("{\"str_value\" : \"s" + i + "\"}\n");
+        }
+        request.setJsonEntity(builder.toString());
+        assertOK(client().performRequest(request));
+        return id;
+    }
+
+    public void testSingleValuedString() throws Exception {
+        IndexingIT.Nodes nodes = IndexingIT.buildNodeAndVersions(client());
+        Version version = nodes.getBWCVersion();
+        // rare_terms was introduced in version 7.3.0
+        assumeTrue("Version too old", version.onOrAfter(Version.V_7_3_0));
+        // increase max buckets
+        setupMaxBuckets();
+        final Settings.Builder settings = Settings.builder()
+            .put(IndexMetadata.INDEX_NUMBER_OF_SHARDS_SETTING.getKey(), 2)
+            .put(IndexMetadata.INDEX_NUMBER_OF_REPLICAS_SETTING.getKey(), 0);
+        createIndex(index, settings.build());
+        // We want to trigger the usage of cuckoo filters that happen only when there are
+        // more than 10k distinct values in one shard.
+        final int numDocs = randomIntBetween(12000, 17000);
+        int id = 1;
+        // Index every value 5 times
+        for (int i = 0; i < 5; i++) {
+            id = indexDocs(numDocs, id);
+            refreshAllIndices();
+        }
+        // There are no rare terms that only appear in one document
+        assertNumRareTerms(1, 0);
+        // All terms have a cardinality lower than 10
+        assertNumRareTerms(10, numDocs);
+    }
+
+    private void assertNumRareTerms(int maxDocs, int rareTerms) throws IOException {
+        final Request request = new Request("POST", index + "/_search");
+        request.setJsonEntity(
+            "{\"aggs\" : {\"rareTerms\" : {\"rare_terms\" : {\"field\" : \"str_value.keyword\", \"max_doc_count\" : " + maxDocs + "}}}}"
+        );
+        final Response response = client().performRequest(request);
+        assertOK(response);
+        final Object o = XContentMapValues.extractValue("aggregations.rareTerms.buckets", responseAsMap(response));
+        assertThat(o, Matchers.instanceOf(List.class));
+        assertThat(((List<?>) o).size(), Matchers.equalTo(rareTerms));
+    }
+}