[Backport 2.19] Fix array_index_out_of_bounds_exception with wildcard and aggregations

CHANGELOG.md

@@ -15,6 +15,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Fixed
 - Harden the circuit breaker and failure handle logic in query result consumer ([#19396](https://github.com/opensearch-project/OpenSearch/pull/19396))
 - Fix case insensitive and escaped query on wildcard ([#16827](https://github.com/opensearch-project/OpenSearch/pull/16827))
+- Fix array_index_out_of_bounds_exception with wildcard and aggregations ([#20842](https://github.com/opensearch-project/OpenSearch/pull/20842))
 
 ### Security
 

server/src/main/java/org/opensearch/index/mapper/WildcardFieldMapper.java

@@ -773,7 +773,7 @@ static class WildcardMatchingQuery extends Query {
         private final Query firstPhaseQuery;
         private final Predicate<String> secondPhaseMatcher;
         private final String patternString; // For toString
-        private final ValueFetcher valueFetcher;
+        private final Supplier<ValueFetcher> valueFetcherSupplier;
         private final SearchLookup searchLookup;
 
         WildcardMatchingQuery(String fieldName, Query firstPhaseQuery, String patternString) {
@@ -794,10 +794,10 @@ public WildcardMatchingQuery(
             this.patternString = Objects.requireNonNull(patternString);
             if (context != null) {
                 this.searchLookup = context.lookup();
-                this.valueFetcher = fieldType.valueFetcher(context, context.lookup(), null);
+                this.valueFetcherSupplier = () -> fieldType.valueFetcher(context, context.lookup(), null);
             } else {
                 this.searchLookup = null;
-                this.valueFetcher = null;
+                this.valueFetcherSupplier = null;
             }
         }
 
@@ -806,14 +806,14 @@ private WildcardMatchingQuery(
             Query firstPhaseQuery,
             Predicate<String> secondPhaseMatcher,
             String patternString,
-            ValueFetcher valueFetcher,
+            Supplier<ValueFetcher> valueFetcherSupplier,
             SearchLookup searchLookup
         ) {
             this.fieldName = fieldName;
             this.firstPhaseQuery = firstPhaseQuery;
             this.secondPhaseMatcher = secondPhaseMatcher;
             this.patternString = patternString;
-            this.valueFetcher = valueFetcher;
+            this.valueFetcherSupplier = valueFetcherSupplier;
             this.searchLookup = searchLookup;
         }
 
@@ -851,7 +851,7 @@ public Query rewrite(IndexSearcher indexSearcher) throws IOException {
                     rewriteFirstPhase,
                     secondPhaseMatcher,
                     patternString,
-                    valueFetcher,
+                    valueFetcherSupplier,
                     searchLookup
                 );
             }
@@ -884,6 +884,9 @@ public Scorer get(long leadCost) throws IOException {
                             Scorer approximateScorer = firstPhaseSupplier.get(leadCost);
                             DocIdSetIterator approximation = approximateScorer.iterator();
                             LeafSearchLookup leafSearchLookup = searchLookup.getLeafSearchLookup(context);
+                            // Create a new ValueFetcher per thread.
+                            // ValueFetcher.setNextReader is not thread safe.
+                            final ValueFetcher valueFetcher = valueFetcherSupplier.get();
                             valueFetcher.setNextReader(context);
 
                             TwoPhaseIterator twoPhaseIterator = new TwoPhaseIterator(approximation) {