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diff --git a/src/mongo/s/config.h b/src/mongo/s/config.h
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+/**
+ *    Copyright (C) 2008-2015 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 <string>
+
+#include "mongo/db/repl/optime.h"
+#include "mongo/platform/atomic_word.h"
+#include "mongo/s/shard_id.h"
+#include "mongo/stdx/mutex.h"
+
+namespace mongo {
+
+class ChunkManager;
+struct CollectionInfo;
+class DatabaseType;
+class OperationContext;
+
+/**
+ * Represents the cache entry for a database.
+ */
+class DBConfig {
+public:
+    DBConfig(const DatabaseType& dbt, repl::OpTime configOpTime);
+    ~DBConfig();
+
+    /**
+     * The name of the database which this entry caches.
+     */
+    const std::string& name() const {
+        return _name;
+    }
+
+    ShardId getPrimaryId();
+
+    /**
+     * Returns whether 'enableSharding' has been called for this database.
+     */
+    bool isShardingEnabled() const {
+        return _shardingEnabled;
+    }
+
+    /**
+     * Removes the specified namespace from the set of collections under this database entry so that
+     * from then onwards it will be treated as unsharded.
+     *
+     * Note that this method doesn't do any writes to the config metadata, but simply drops the
+     * specified namespace from the cache.
+     */
+    void markNSNotSharded(const std::string& ns);
+
+    /**
+     * @return whether or not the 'ns' collection is partitioned
+     */
+    bool isSharded(const std::string& ns);
+
+    std::shared_ptr<ChunkManager> getChunkManager(OperationContext* opCtx,
+                                                  const std::string& ns,
+                                                  bool reload = false,
+                                                  bool forceReload = false);
+    std::shared_ptr<ChunkManager> getChunkManagerIfExists(OperationContext* opCtx,
+                                                          const std::string& ns,
+                                                          bool reload = false,
+                                                          bool forceReload = false);
+
+    /**
+     * Returns true if it is successful at loading the DBConfig, false if the database is not found,
+     * and throws on all other errors.
+     */
+    bool load(OperationContext* opCtx);
+
+protected:
+    typedef std::map<std::string, CollectionInfo> CollectionInfoMap;
+    typedef AtomicUInt64::WordType Counter;
+
+    /**
+     * Returns true if it is successful at loading the DBConfig, false if the database is not found,
+     * and throws on all other errors.
+     * Also returns true without reloading if reloadIteration is not equal to the _reloadCount.
+     * This is to avoid multiple threads attempting to reload do duplicate work.
+     */
+    bool _loadIfNeeded(OperationContext* opCtx, Counter reloadIteration);
+
+    // All member variables are labeled with one of the following codes indicating the
+    // synchronization rules for accessing them.
+    //
+    // (L) Must hold _lock for access.
+    // (S) Self synchronizing, no explicit locking needed.
+    //
+    // Mutex lock order:
+    // _hitConfigServerLock -> _lock
+    //
+
+    // Name of the database which this entry caches
+    const std::string _name;
+
+    // Whether sharding is enabled for this database
+    const bool _shardingEnabled;
+
+    // Primary shard id
+    ShardId _primaryId;  // (L)
+
+    // Set of collections and lock to protect access
+    stdx::mutex _lock;
+    CollectionInfoMap _collections;  // (L)
+
+    // OpTime of config server when the database definition was loaded.
+    repl::OpTime _configOpTime;  // (L)
+
+    // Ensures that only one thread at a time loads collection configuration data from
+    // the config server
+    stdx::mutex _hitConfigServerLock;
+
+    // Increments every time this performs a full reload. Since a full reload can take a very
+    // long time for very large clusters, this can be used to minimize duplicate work when multiple
+    // threads tries to perform full rerload at roughly the same time.
+    AtomicUInt64 _reloadCount;  // (S)
+};
+
+}  // namespace mongo