Automatically early terminate search query based on index sorting (#24864)

This commit refactors the query phase in order to be able
to automatically detect queries that can be early terminated.
If the index sort matches the query sort, the top docs collection is early terminated
on each segment and the computing of the total number of hits that match the query is delegated to a simple TotalHitCountCollector.
This change also adds a new parameter to the search request called `track_total_hits`.
It indicates if the total number of hits that match the query should be tracked.
If false, queries sorted by the index sort will not try to compute this information and 
and will limit the collection to the first N documents per segment.
Aggregations are not impacted and will continue to see every document
even when the index sort matches the query sort and `track_total_hits` is false.

Relates #6720

2 files changed, 29 insertions, 7 deletions

diff --git a/test/framework/src/main/java/org/elasticsearch/search/RandomSearchRequestGenerator.java b/test/framework/src/main/java/org/elasticsearch/search/RandomSearchRequestGenerator.java
index 4cd46fe507..e4f5f2cc39 100644
--- a/test/framework/src/main/java/org/elasticsearch/search/RandomSearchRequestGenerator.java
+++ b/test/framework/src/main/java/org/elasticsearch/search/RandomSearchRequestGenerator.java
@@ -143,6 +143,9 @@ public class RandomSearchRequestGenerator {
         if (randomBoolean()) {
             builder.terminateAfter(randomIntBetween(1, 100000));
         }
+        if (randomBoolean()) {
+            builder.trackTotalHits(randomBoolean());
+        }
 
         switch(randomInt(2)) {
             case 0:
diff --git a/test/framework/src/main/java/org/elasticsearch/test/TestSearchContext.java b/test/framework/src/main/java/org/elasticsearch/test/TestSearchContext.java
index f77414e7d5..038a21c28e 100644
--- a/test/framework/src/main/java/org/elasticsearch/test/TestSearchContext.java
+++ b/test/framework/src/main/java/org/elasticsearch/test/TestSearchContext.java
@@ -60,6 +60,7 @@ import org.elasticsearch.search.sort.SortAndFormats;
 import org.elasticsearch.search.suggest.SuggestionSearchContext;
 import org.elasticsearch.threadpool.ThreadPool;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -81,11 +82,15 @@ public class TestSearchContext extends SearchContext {
     Query query;
     Float minScore;
     SearchTask task;
+    SortAndFormats sort;
+    boolean trackScores = false;
+    boolean trackTotalHits = true;
 
     ContextIndexSearcher searcher;
     int size;
     private int terminateAfter = DEFAULT_TERMINATE_AFTER;
     private SearchContextAggregations aggregations;
+    private ScrollContext scrollContext;
 
     private final long originNanoTime = System.nanoTime();
     private final Map<String, SearchExtBuilder> searchExtBuilders = new HashMap<>();
@@ -161,12 +166,13 @@ public class TestSearchContext extends SearchContext {
 
     @Override
     public ScrollContext scrollContext() {
-        return null;
+        return scrollContext;
     }
 
     @Override
     public SearchContext scrollContext(ScrollContext scrollContext) {
-        throw new UnsupportedOperationException();
+        this.scrollContext = scrollContext;
+        return this;
     }
 
     @Override
@@ -210,7 +216,7 @@ public class TestSearchContext extends SearchContext {
 
     @Override
     public List<RescoreSearchContext> rescore() {
-        return null;
+        return Collections.emptyList();
     }
 
     @Override
@@ -336,22 +342,35 @@ public class TestSearchContext extends SearchContext {
 
     @Override
     public SearchContext sort(SortAndFormats sort) {
-        return null;
+        this.sort = sort;
+        return this;
     }
 
     @Override
     public SortAndFormats sort() {
-        return null;
+        return sort;
     }
 
     @Override
     public SearchContext trackScores(boolean trackScores) {
-        return null;
+        this.trackScores = trackScores;
+        return this;
     }
 
     @Override
     public boolean trackScores() {
-        return false;
+        return trackScores;
+    }
+
+    @Override
+    public SearchContext trackTotalHits(boolean trackTotalHits) {
+        this.trackTotalHits = trackTotalHits;
+        return this;
+    }
+
+    @Override
+    public boolean trackTotalHits() {
+        return trackTotalHits;
     }
 
     @Override