SERVER-14102 implement the explain command on mongos

1 files changed, 85 insertions, 0 deletions

diff --git a/src/mongo/db/query/explain_common.h b/src/mongo/db/query/explain_common.h
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+++ b/src/mongo/db/query/explain_common.h
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+/**
+ *    Copyright (C) 2013-2014 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    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
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    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 GNU Affero General 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/base/status.h"
+#include "mongo/bson/bsonobj.h"
+
+namespace mongo {
+
+    /**
+     * Utilities used for explain implementations on both mongod and mongos.
+     */
+    class ExplainCommon {
+    public:
+        /**
+         * The various supported verbosity levels for explain. The order is
+         * significant: the enum values are assigned in order of increasing verbosity.
+         */
+        enum Verbosity {
+            // At all verbosities greater than or equal to QUERY_PLANNER, we display information
+            // about the plan selected and alternate rejected plans. Does not include any execution-
+            // related info. String alias is "queryPlanner".
+            QUERY_PLANNER = 0,
+
+            // At all verbosities greater than or equal to EXEC_STATS, we display a section of
+            // output containing both overall execution stats, and stats per stage in the
+            // execution tree. String alias is "execStats".
+            EXEC_STATS = 1,
+
+            // At this second-highest verbosity level, we generate the execution stats for each
+            // rejected plan as well as the winning plan. String alias is "allPlansExecution".
+            EXEC_ALL_PLANS = 2,
+
+            // This is the highest verbosity level. It has the same behavior as EXEC_ALL_PLANS,
+            // except it includes more detailed stats. String alias is "full".
+            //
+            // The FULL verbosity level is used to generate detailed debug information for the
+            // plan cache and for logging. It includes metrics like "works", "isEOF", and "advanced"
+            // that are omitted at lesser verbosities.
+            FULL = 3,
+        };
+
+        /**
+         * Converts an explain verbosity to its string representation.
+         */
+        static const char* verbosityString(ExplainCommon::Verbosity verbosity);
+
+        /**
+         * Does some basic validation of the command BSON, and retrieves the explain verbosity.
+         *
+         * Returns a non-OK status if parsing fails.
+         *
+         * On success, populates "verbosity".
+         */
+        static Status parseCmdBSON(const BSONObj& cmdObj, ExplainCommon::Verbosity* verbosity);
+
+    };
+
+} // namespace