add changelog

Signed-off-by: bowenlan-amzn <bowenlan23@gmail.com>

CHANGELOG.md

@@ -165,6 +165,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Improve boolean parsing performance ([#11308](https://github.com/opensearch-project/OpenSearch/pull/11308))
 - Interpret byte array as primitive using VarHandles ([#11362](https://github.com/opensearch-project/OpenSearch/pull/11362))
 - Change error message when per shard document limit is breached ([#11312](https://github.com/opensearch-project/OpenSearch/pull/11312))
+- Apply the fast filter optimization to composite aggregation ([#11505](https://github.com/opensearch-project/OpenSearch/pull/11505))
 
 ### Deprecated
 

server/src/main/java/org/opensearch/search/aggregations/bucket/FilterRewriteHelper.java

@@ -248,7 +248,7 @@ public static class ValueSourceContext {
          * @param missing   whether missing value/bucket is set
          * @param hasScript whether script is used
          * @param fieldType null if the field doesn't exist
-         * @param afterKey
+         * @param afterKey  for composite aggregation, the key of the last bucket in the previous response
          */
         public ValueSourceContext(boolean missing, boolean hasScript, MappedFieldType fieldType, long afterKey) {
             this.missing = missing;

server/src/main/java/org/opensearch/search/aggregations/bucket/composite/CompositeAggregator.java

@@ -602,7 +602,7 @@ public void collect(int doc, long bucket) throws IOException {
                 try {
                     long docCount = docCountProvider.getDocCount(doc);
                     if (queue.addIfCompetitive(indexSortPrefix, docCount)) {
-                        if (builder != null && lastDoc != doc) { // TODO reading how can lastDoc == doc?
+                        if (builder != null && lastDoc != doc) {
                             builder.add(doc);
                             lastDoc = doc;
                         }