[9.0] Return an empty suggestion when suggest phase times out (#122575)

docs/changelog/122575.yaml

@@ -0,0 +1,6 @@
+pr: 122575
+summary: Return an empty suggestion when suggest phase times out
+area: Suggesters
+type: bug
+issues:
+ - 122548

muted-tests.yml

@@ -323,9 +323,6 @@ tests:
 - class: org.elasticsearch.compute.operator.exchange.ExchangeServiceTests
   method: testExchangeSourceContinueOnFailure
   issue: https://github.com/elastic/elasticsearch/issues/122408
-- class: org.elasticsearch.search.SearchTimeoutIT
-  method: testSuggestTimeoutWithPartialResults
-  issue: https://github.com/elastic/elasticsearch/issues/122548
 - class: org.elasticsearch.repositories.blobstore.testkit.analyze.MinioRepositoryAnalysisRestIT
   method: testRepositoryAnalysis
   issue: https://github.com/elastic/elasticsearch/issues/122670

server/src/internalClusterTest/java/org/elasticsearch/search/SearchTimeoutIT.java

@@ -484,8 +484,7 @@ protected TermSuggestion innerExecute(
             CharsRefBuilder spare
         ) {
             contextIndexSearcher.throwTimeExceededException();
-            assert false;
-            return new TermSuggestion(name, suggestion.getSize(), SortBy.SCORE);
+            throw new AssertionError("should have thrown TimeExceededException");
         }
 
         @Override

server/src/main/java/org/elasticsearch/search/query/QueryPhase.java

@@ -126,15 +126,7 @@ static void executeRank(SearchContext searchContext) throws QueryPhaseExecutionE
 
     static void executeQuery(SearchContext searchContext) throws QueryPhaseExecutionException {
         if (searchContext.hasOnlySuggest()) {
-            try {
-                SuggestPhase.execute(searchContext);
-            } catch (ContextIndexSearcher.TimeExceededException timeExceededException) {
-                SearchTimeoutException.handleTimeout(
-                    searchContext.request().allowPartialSearchResults(),
-                    searchContext.shardTarget(),
-                    searchContext.queryResult()
-                );
-            }
+            SuggestPhase.execute(searchContext);
             searchContext.queryResult().topDocs(new TopDocsAndMaxScore(Lucene.EMPTY_TOP_DOCS, Float.NaN), new DocValueFormat[0]);
             return;
         }
@@ -150,18 +142,10 @@ static void executeQuery(SearchContext searchContext) throws QueryPhaseExecution
 
         addCollectorsAndSearch(searchContext);
 
-        try {
-            RescorePhase.execute(searchContext);
-            SuggestPhase.execute(searchContext);
-            if (searchContext.getProfilers() != null) {
-                searchContext.queryResult().profileResults(searchContext.getProfilers().buildQueryPhaseResults());
-            }
-        } catch (ContextIndexSearcher.TimeExceededException timeExceededException) {
-            SearchTimeoutException.handleTimeout(
-                searchContext.request().allowPartialSearchResults(),
-                searchContext.shardTarget(),
-                searchContext.queryResult()
-            );
+        RescorePhase.execute(searchContext);
+        SuggestPhase.execute(searchContext);
+        if (searchContext.getProfilers() != null) {
+            searchContext.queryResult().profileResults(searchContext.getProfilers().buildQueryPhaseResults());
         }
     }
 

server/src/main/java/org/elasticsearch/search/rescore/RescorePhase.java

@@ -18,7 +18,9 @@
 import org.elasticsearch.common.lucene.search.TopDocsAndMaxScore;
 import org.elasticsearch.common.util.Maps;
 import org.elasticsearch.lucene.grouping.TopFieldGroups;
+import org.elasticsearch.search.internal.ContextIndexSearcher;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.query.SearchTimeoutException;
 import org.elasticsearch.search.sort.ShardDocSortField;
 import org.elasticsearch.search.sort.SortAndFormats;
 
@@ -84,6 +86,13 @@ public static void execute(SearchContext context) {
                 .topDocs(new TopDocsAndMaxScore(topDocs, topDocs.scoreDocs[0].score), context.queryResult().sortValueFormats());
         } catch (IOException e) {
             throw new ElasticsearchException("Rescore Phase Failed", e);
+        } catch (ContextIndexSearcher.TimeExceededException timeExceededException) {
+            SearchTimeoutException.handleTimeout(
+                context.request().allowPartialSearchResults(),
+                context.shardTarget(),
+                context.queryResult()
+            );
+            // if the rescore phase times out and partial results are allowed, the returned top docs from this shard won't be rescored
         }
     }
 

server/src/main/java/org/elasticsearch/search/suggest/SuggestPhase.java

@@ -10,7 +10,9 @@
 
 import org.apache.lucene.util.CharsRefBuilder;
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.search.internal.ContextIndexSearcher;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.query.SearchTimeoutException;
 import org.elasticsearch.search.suggest.Suggest.Suggestion;
 import org.elasticsearch.search.suggest.Suggest.Suggestion.Entry;
 import org.elasticsearch.search.suggest.Suggest.Suggestion.Entry.Option;
@@ -40,12 +42,17 @@ public static void execute(SearchContext context) {
             for (Map.Entry<String, SuggestionSearchContext.SuggestionContext> entry : suggest.suggestions().entrySet()) {
                 SuggestionSearchContext.SuggestionContext suggestion = entry.getValue();
                 Suggester<SuggestionContext> suggester = suggestion.getSuggester();
-                Suggestion<? extends Entry<? extends Option>> result = suggester.execute(
-                    entry.getKey(),
-                    suggestion,
-                    context.searcher(),
-                    spare
-                );
+                Suggestion<? extends Entry<? extends Option>> result;
+                try {
+                    result = suggester.execute(entry.getKey(), suggestion, context.searcher(), spare);
+                } catch (ContextIndexSearcher.TimeExceededException timeExceededException) {
+                    SearchTimeoutException.handleTimeout(
+                        context.request().allowPartialSearchResults(),
+                        context.shardTarget(),
+                        context.queryResult()
+                    );
+                    result = suggester.emptySuggestion(entry.getKey(), suggestion, spare);
+                }
                 if (result != null) {
                     assert entry.getKey().equals(result.name);
                     suggestions.add(result);

server/src/test/java/org/elasticsearch/search/query/QueryPhaseTimeoutTests.java

@@ -297,7 +297,8 @@ public void testSuggestOnlyWithTimeout() throws Exception {
             assertTrue(context.hasOnlySuggest());
             QueryPhase.execute(context);
             assertTrue(context.queryResult().searchTimedOut());
-            assertNull(context.queryResult().suggest());
+            assertEquals(1, context.queryResult().suggest().size());
+            assertEquals(0, context.queryResult().suggest().getSuggestion("suggestion").getEntries().size());
             assertNotNull(context.queryResult().topDocs());
             assertEquals(0, context.queryResult().topDocs().topDocs.totalHits.value());
         }
@@ -311,7 +312,8 @@ public void testSuggestAndQueryWithSuggestTimeout() throws Exception {
             QueryPhase.execute(context);
             assertThat(context.queryResult().topDocs().topDocs.totalHits.value(), Matchers.greaterThan(0L));
             assertTrue(context.queryResult().searchTimedOut());
-            assertNull(context.queryResult().suggest());
+            assertEquals(1, context.queryResult().suggest().size());
+            assertEquals(0, context.queryResult().suggest().getSuggestion("suggestion").getEntries().size());
         }
     }