SERVER-38691 Include serverInfo in explain output for aggregation and sharding

7 files changed, 109 insertions, 21 deletions

diff --git a/src/mongo/db/query/SConscript b/src/mongo/db/query/SConscript
index 4e21c1b2417..b39bf5d553d 100644
--- a/src/mongo/db/query/SConscript
+++ b/src/mongo/db/query/SConscript
@@ -85,6 +85,7 @@ env.Library(
 env.Library(
     target="query_common",
     source=[
+        "explain_common.cpp",
         "find_common.cpp",
         "parsed_distinct.cpp",
     ],
diff --git a/src/mongo/db/query/explain.cpp b/src/mongo/db/query/explain.cpp
index 3466e16240c..9fa426ad53b 100644
--- a/src/mongo/db/query/explain.cpp
+++ b/src/mongo/db/query/explain.cpp
@@ -47,6 +47,7 @@
 #include "mongo/db/keypattern.h"
 #include "mongo/db/query/canonical_query_encoder.h"
 #include "mongo/db/query/collection_query_info.h"
+#include "mongo/db/query/explain_common.h"
 #include "mongo/db/query/get_executor.h"
 #include "mongo/db/query/plan_executor.h"
 #include "mongo/db/query/plan_summary_stats.h"
@@ -757,17 +758,6 @@ void Explain::generateSinglePlanExecutionInfo(const PlanStageStats* stats,
     stagesBob.doneFast();
 }
 
-// static
-void Explain::generateServerInfo(BSONObjBuilder* out) {
-    BSONObjBuilder serverBob(out->subobjStart("serverInfo"));
-    out->append("host", getHostNameCached());
-    out->appendNumber("port", serverGlobalParams.port);
-    auto&& vii = VersionInfoInterface::instance();
-    out->append("version", vii.version());
-    out->append("gitVersion", vii.gitVersion());
-    serverBob.doneFast();
-}
-
 std::unique_ptr<PlanStageStats> Explain::getWinningPlanTrialStats(PlanExecutor* exec) {
     // Inspect the tree to see if there is a MultiPlanStage. Plan selection has already happened at
     // this point, since we have a PlanExecutor.
@@ -877,6 +867,8 @@ void Explain::explainPipelineExecutor(PlanExecutor* exec,
     }
 
     *out << "stages" << Value(pps->writeExplainOps(verbosity));
+
+    explain_common::generateServerInfo(out);
 }
 
 // static
@@ -909,7 +901,7 @@ void Explain::explainStages(PlanExecutor* exec,
                   extraInfo,
                   out);
 
-    generateServerInfo(out);
+    explain_common::generateServerInfo(out);
 }
 
 // static
diff --git a/src/mongo/db/query/explain.h b/src/mongo/db/query/explain.h
index e6ad7cc0c5c..2fff62ac1d2 100644
--- a/src/mongo/db/query/explain.h
+++ b/src/mongo/db/query/explain.h
@@ -236,14 +236,6 @@ private:
                                       Status executePlanStatus,
                                       PlanStageStats* winningPlanTrialStats,
                                       BSONObjBuilder* out);
-
-    /**
-     * Adds the 'serverInfo' explain section to the BSON object being build
-     * by 'out'.
-     *
-     * This is a helper for generating explain BSON. It is used by explainStages(...).
-     */
-    static void generateServerInfo(BSONObjBuilder* out);
 };
 
 }  // namespace mongo
diff --git a/src/mongo/db/query/explain_common.cpp b/src/mongo/db/query/explain_common.cpp
new file mode 100644
index 00000000000..01242acf6fd
--- /dev/null
+++ b/src/mongo/db/query/explain_common.cpp
@@ -0,0 +1,50 @@
+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/query/explain_common.h"
+
+#include "mongo/db/server_options.h"
+#include "mongo/util/net/socket_utils.h"
+#include "mongo/util/version.h"
+
+namespace mongo::explain_common {
+
+void generateServerInfo(BSONObjBuilder* out) {
+    BSONObjBuilder serverBob(out->subobjStart("serverInfo"));
+    out->append("host", getHostNameCached());
+    out->appendNumber("port", serverGlobalParams.port);
+    auto&& vii = VersionInfoInterface::instance();
+    out->append("version", vii.version());
+    out->append("gitVersion", vii.gitVersion());
+    serverBob.doneFast();
+}
+
+}  // namespace mongo::explain_common
diff --git a/src/mongo/db/query/explain_common.h b/src/mongo/db/query/explain_common.h
new file mode 100644
index 00000000000..d9b035beb8f
--- /dev/null
+++ b/src/mongo/db/query/explain_common.h
@@ -0,0 +1,46 @@
+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/bson/bsonobjbuilder.h"
+
+/**
+ * Namespace for static methods that are shared between explain on mongod and on mongos.
+ */
+namespace mongo::explain_common {
+
+/**
+ * Adds the 'serverInfo' explain section to the BSON object being built by 'out'.
+ *
+ * This section include the host, port, version, and gitVersion.
+ */
+void generateServerInfo(BSONObjBuilder* out);
+
+}  // namespace mongo::explain_common
diff --git a/src/mongo/s/commands/cluster_explain.cpp b/src/mongo/s/commands/cluster_explain.cpp
index 3082a34fc7b..ce55b18d38d 100644
--- a/src/mongo/s/commands/cluster_explain.cpp
+++ b/src/mongo/s/commands/cluster_explain.cpp
@@ -32,6 +32,7 @@
 #include "mongo/bson/bsonmisc.h"
 #include "mongo/db/command_generic_argument.h"
 #include "mongo/db/commands.h"
+#include "mongo/db/query/explain_common.h"
 #include "mongo/rpc/get_status_from_command_result.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/commands/cluster_explain.h"
@@ -356,6 +357,7 @@ Status ClusterExplain::buildExplainResult(OperationContext* opCtx,
 
     buildPlannerInfo(opCtx, shardResults, mongosStageName, out);
     buildExecStats(shardResults, mongosStageName, millisElapsed, out);
+    explain_common::generateServerInfo(out);
 
     return Status::OK();
 }
diff --git a/src/mongo/s/query/cluster_aggregate.cpp b/src/mongo/s/query/cluster_aggregate.cpp
index 4696181c003..972628a1498 100644
--- a/src/mongo/s/query/cluster_aggregate.cpp
+++ b/src/mongo/s/query/cluster_aggregate.cpp
@@ -50,6 +50,7 @@
 #include "mongo/db/pipeline/sharded_agg_helpers.h"
 #include "mongo/db/query/collation/collator_factory_interface.h"
 #include "mongo/db/query/cursor_response.h"
+#include "mongo/db/query/explain_common.h"
 #include "mongo/db/query/find_common.h"
 #include "mongo/db/views/resolved_view.h"
 #include "mongo/db/views/view.h"
@@ -208,6 +209,10 @@ Status ClusterAggregate::runAggregate(OperationContext* opCtx,
     }
 
     auto targeter = std::move(targetingStatus.getValue());
+    if (request.getExplain()) {
+        explain_common::generateServerInfo(result);
+    }
+
     switch (targeter.policy) {
         case sharded_agg_helpers::AggregationTargeter::TargetingPolicy::kPassthrough: {
             // A pipeline with $changeStream should never be allowed to passthrough.
@@ -222,8 +227,8 @@ Status ClusterAggregate::runAggregate(OperationContext* opCtx,
         }
 
         case sharded_agg_helpers::AggregationTargeter::TargetingPolicy::kMongosRequired: {
-            auto expCtx = targeter.pipeline->getContext();
             // If this is an explain write the explain output and return.
+            auto expCtx = targeter.pipeline->getContext();
             if (expCtx->explain) {
                 *result << "splitPipeline" << BSONNULL << "mongos"
                         << Document{