From 0acf74420c1322687a6857c46043377384b05100 Mon Sep 17 00:00:00 2001
From: Jim Ferenczi <jim.ferenczi@elastic.co>
Date: Thu, 28 Sep 2017 13:57:10 +0200
Subject: [PATCH] Change VersionFetchSubPhase to create doc values iterator
 once per segment (#26809)

---
 .../fetch/subphase/VersionFetchSubPhase.java  | 33 +++++++++++++------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/core/src/main/java/org/elasticsearch/search/fetch/subphase/VersionFetchSubPhase.java b/core/src/main/java/org/elasticsearch/search/fetch/subphase/VersionFetchSubPhase.java
index 5f69230ca42..baa0c6e9551 100644
--- a/core/src/main/java/org/elasticsearch/search/fetch/subphase/VersionFetchSubPhase.java
+++ b/core/src/main/java/org/elasticsearch/search/fetch/subphase/VersionFetchSubPhase.java
@@ -18,32 +18,45 @@
  */
 package org.elasticsearch.search.fetch.subphase;
 
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.NumericDocValues;
-import org.elasticsearch.ElasticsearchException;
+import org.apache.lucene.index.ReaderUtil;
 import org.elasticsearch.common.lucene.uid.Versions;
 import org.elasticsearch.index.mapper.VersionFieldMapper;
+import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.search.fetch.FetchSubPhase;
 import org.elasticsearch.search.internal.SearchContext;
 
 import java.io.IOException;
+import java.util.Arrays;
+import java.util.Comparator;
 
 public final class VersionFetchSubPhase implements FetchSubPhase {
-
     @Override
-    public void hitExecute(SearchContext context, HitContext hitContext) {
+    public void hitsExecute(SearchContext context, SearchHit[] hits) throws IOException {
         if (context.version() == false ||
             (context.storedFieldsContext() != null && context.storedFieldsContext().fetchFields() == false)) {
             return;
         }
-        long version = Versions.NOT_FOUND;
-        try {
-            NumericDocValues versions = hitContext.reader().getNumericDocValues(VersionFieldMapper.NAME);
-            if (versions != null && versions.advanceExact(hitContext.docId())) {
+
+        hits = hits.clone(); // don't modify the incoming hits
+        Arrays.sort(hits, Comparator.comparingInt(SearchHit::docId));
+
+        int lastReaderId = -1;
+        NumericDocValues versions = null;
+        for (SearchHit hit : hits) {
+            int readerId = ReaderUtil.subIndex(hit.docId(), context.searcher().getIndexReader().leaves());
+            LeafReaderContext subReaderContext = context.searcher().getIndexReader().leaves().get(readerId);
+            if (lastReaderId != readerId) {
+                versions = subReaderContext.reader().getNumericDocValues(VersionFieldMapper.NAME);
+                lastReaderId = readerId;
+            }
+            int docId = hit.docId() - subReaderContext.docBase;
+            long version = Versions.NOT_FOUND;
+            if (versions != null && versions.advanceExact(docId)) {
                 version = versions.longValue();
             }
-        } catch (IOException e) {
-            throw new ElasticsearchException("Could not retrieve version", e);
+            hit.version(version < 0 ? -1 : version);
         }
-        hitContext.hit().version(version < 0 ? -1 : version);
     }
 }