Add forked field comparator that uses doc values skippers for seqno field when fetching ops.

Author: martijnvg

server/src/main/java/org/elasticsearch/common/lucene/search/XLongComparator.java

@@ -0,0 +1,111 @@
+/*
+ * 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", the "GNU Affero General Public License v3.0 only", 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", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.common.lucene.search;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.search.LeafFieldComparator;
+import org.apache.lucene.search.Pruning;
+import org.apache.lucene.search.comparators.LongComparator;
+import org.apache.lucene.util.NumericUtils;
+
+import java.io.IOException;
+
+// TODO: remove once upgrading to Lucene 10.3, see base class why.
+public class XLongComparator extends XNumericComparator<Long> {
+
+    private final long[] values;
+    protected long topValue;
+    protected long bottom;
+
+    public XLongComparator(int numHits, String field, Long missingValue, boolean reverse, Pruning pruning) {
+        super(field, missingValue != null ? missingValue : 0L, reverse, pruning, Long.BYTES);
+        values = new long[numHits];
+    }
+
+    @Override
+    public int compare(int slot1, int slot2) {
+        return Long.compare(values[slot1], values[slot2]);
+    }
+
+    @Override
+    public void setTopValue(Long value) {
+        super.setTopValue(value);
+        topValue = value;
+    }
+
+    @Override
+    public Long value(int slot) {
+        return Long.valueOf(values[slot]);
+    }
+
+    @Override
+    protected long missingValueAsComparableLong() {
+        return missingValue;
+    }
+
+    @Override
+    protected long sortableBytesToLong(byte[] bytes) {
+        return NumericUtils.sortableBytesToLong(bytes, 0);
+    }
+
+    @Override
+    public LeafFieldComparator getLeafComparator(LeafReaderContext context) throws IOException {
+        return new XLongComparator.LongLeafComparator(context);
+    }
+
+    /** Leaf comparator for {@link LongComparator} that provides skipping functionality */
+    public class LongLeafComparator extends XNumericComparator<Long>.NumericLeafComparator {
+
+        public LongLeafComparator(LeafReaderContext context) throws IOException {
+            super(context);
+        }
+
+        private long getValueForDoc(int doc) throws IOException {
+            if (docValues.advanceExact(doc)) {
+                return docValues.longValue();
+            } else {
+                return missingValue;
+            }
+        }
+
+        @Override
+        public void setBottom(int slot) throws IOException {
+            bottom = values[slot];
+            super.setBottom(slot);
+        }
+
+        @Override
+        public int compareBottom(int doc) throws IOException {
+            return Long.compare(bottom, getValueForDoc(doc));
+        }
+
+        @Override
+        public int compareTop(int doc) throws IOException {
+            return Long.compare(topValue, getValueForDoc(doc));
+        }
+
+        @Override
+        public void copy(int slot, int doc) throws IOException {
+            values[slot] = getValueForDoc(doc);
+            super.copy(slot, doc);
+        }
+
+        @Override
+        protected long bottomAsComparableLong() {
+            return bottom;
+        }
+
+        @Override
+        protected long topAsComparableLong() {
+            return topValue;
+        }
+    }
+
+}