Add some Javadocs to TransportSearchAction and adjacent classes. (#110733)

Author: smalyshev

server/src/main/java/org/elasticsearch/action/ResolvedIndices.java

@@ -27,6 +27,10 @@
 import java.util.Map;
 import java.util.Set;
 
+/**
+ * Container for information about results of the resolution of index expression.
+ * Contains local indices, map of remote indices and metadata.
+ */
 public class ResolvedIndices {
     @Nullable
     private final SearchContextId searchContextId;

server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java

@@ -711,6 +711,7 @@ static SearchResponseMerger createSearchResponseMerger(
     }
 
     /**
+     * Collect remote search shards that we need to search for potential matches.
      * Used for ccs_minimize_roundtrips=false
      */
     static void collectSearchShards(
@@ -988,6 +989,10 @@ static BiFunction<String, String, DiscoveryNode> getRemoteClusterNodeLookup(Map<
         };
     }
 
+    /**
+     * Produce a list of {@link SearchShardIterator}s from the set of responses from remote clusters.
+     * Used for ccs_minimize_roundtrips=false.
+     */
     static List<SearchShardIterator> getRemoteShardsIterator(
         Map<String, SearchShardsResponse> searchShardsResponses,
         Map<String, OriginalIndices> remoteIndicesByCluster,
@@ -1085,6 +1090,9 @@ private static boolean checkAllRemotePITShardsWereReturnedBySearchShards(
             .allMatch(searchContextIdForNode -> searchContextIdForNode.getClusterAlias() == null);
     }
 
+    /**
+     * If any of the indices we are searching are frozen, issue deprecation warning.
+     */
     void frozenIndexCheck(ResolvedIndices resolvedIndices) {
         List<String> frozenIndices = new ArrayList<>();
         Map<Index, IndexMetadata> indexMetadataMap = resolvedIndices.getConcreteLocalIndicesMetadata();
@@ -1104,6 +1112,10 @@ void frozenIndexCheck(ResolvedIndices resolvedIndices) {
         }
     }
 
+    /**
+     * Execute search locally and for all given remote shards.
+     * Used when minimize_roundtrips=false or for local search.
+     */
     private void executeSearch(
         SearchTask task,
         SearchTimeProvider timeProvider,
@@ -1500,6 +1512,11 @@ private static void failIfOverShardCountLimit(ClusterService clusterService, int
         }
     }
 
+    /**
+     * {@link ActionListener} suitable for collecting cross-cluster responses.
+     * @param <Response> Response type we're getting as intermediate per-cluster results.
+     * @param <FinalResponse> Response type that the final listener expects.
+     */
     abstract static class CCSActionListener<Response, FinalResponse> implements ActionListener<Response> {
         protected final String clusterAlias;
         protected final boolean skipUnavailable;
@@ -1533,6 +1550,9 @@ public final void onResponse(Response response) {
             maybeFinish();
         }
 
+        /**
+         * Specific listener type will implement this method to process its specific partial response.
+         */
         abstract void innerOnResponse(Response response);
 
         @Override
@@ -1670,6 +1690,10 @@ static List<SearchShardIterator> getLocalLocalShardsIteratorFromPointInTime(
         return iterators;
     }
 
+    /**
+     * Create a list of {@link SearchShardIterator}s for the local indices we are searching.
+     * This resolves aliases and index expressions.
+     */
     List<SearchShardIterator> getLocalShardsIterator(
         ClusterState clusterState,
         SearchRequest searchRequest,

server/src/main/java/org/elasticsearch/rest/action/search/SearchResponseMetrics.java

@@ -14,6 +14,9 @@
 
 import java.util.Map;
 
+/**
+ * Container class for aggregated metrics about search responses.
+ */
 public class SearchResponseMetrics {
 
     public enum ResponseCountTotalStatus {