SERVER-22359 Introduce per collection sharding state

Author: kaloianm

src/mongo/db/s/SConscript

@@ -36,6 +36,7 @@ env.Library(
     target='sharding',
     source=[
         'chunk_move_write_concern_options.cpp',
+        'collection_sharding_state.cpp',
         'migration_destination_manager.cpp',
         'migration_impl.cpp',
         'migration_source_manager.cpp',

src/mongo/db/s/collection_sharding_state.cpp

@@ -0,0 +1,63 @@
+/**
+ *    Copyright (C) 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.
+ */
+
+#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/s/collection_sharding_state.h"
+
+#include "mongo/db/concurrency/lock_state.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/db/s/collection_metadata.h"
+#include "mongo/db/s/sharding_state.h"
+#include "mongo/s/chunk_version.h"
+
+namespace mongo {
+
+CollectionShardingState::CollectionShardingState(
+    NamespaceString nss, std::unique_ptr<CollectionMetadata> initialMetadata)
+    : _nss(std::move(nss)), _metadata(std::move(initialMetadata)) {}
+
+CollectionShardingState::~CollectionShardingState() = default;
+
+CollectionShardingState* CollectionShardingState::get(OperationContext* txn,
+                                                      const std::string& ns) {
+    // Collection lock must be held to have a reference to the collection's sharding state
+    dassert(txn->lockState()->isCollectionLockedForMode(ns, MODE_IS));
+
+    ShardingState* const shardingState = ShardingState::get(txn);
+    return shardingState->getNS(ns);
+}
+
+void CollectionShardingState::setMetadata(std::shared_ptr<CollectionMetadata> newMetadata) {
+    invariant(newMetadata);
+    _metadata = std::move(newMetadata);
+}
+
+}  // namespace mongo

src/mongo/db/s/collection_sharding_state.h

@@ -0,0 +1,91 @@
+/**
+ *    Copyright (C) 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/base/disallow_copying.h"
+#include "mongo/base/string_data.h"
+#include "mongo/db/namespace_string.h"
+
+namespace mongo {
+
+class BSONObj;
+class CollectionMetadata;
+class OperationContext;
+
+/**
+ * Contains all sharding-related runtime state for a given collection. One such object is assigned
+ * to each sharded collection known on a mongod instance. A set of these objects is linked off the
+ * instance's sharding state.
+ *
+ * Synchronization rules: In order to look-up this object in the instance's sharding map, one must
+ * have some lock on the respective collection.
+ */
+class CollectionShardingState {
+    MONGO_DISALLOW_COPYING(CollectionShardingState);
+
+public:
+    /**
+     * Instantiates a new per-collection sharding state with some initial metadata.
+     */
+    CollectionShardingState(NamespaceString nss,
+                            std::unique_ptr<CollectionMetadata> initialMetadata);
+    ~CollectionShardingState();
+
+    /**
+     * Obtains the sharding state for the specified collection. If it does not exist, it will be
+     * created and will remain active until the collection is dropped or unsharded.
+     *
+     * Must be called with some lock held on the specific collection being looked up and the
+     * returned pointer should never be stored.
+     */
+    static CollectionShardingState* get(OperationContext* txn, const std::string& ns);
+
+    /**
+     * Returns the chunk metadata for the collection.
+     */
+    std::shared_ptr<CollectionMetadata> getMetadata() const {
+        return _metadata;
+    }
+
+    /**
+     * Set a new metadata to be used for this collection.
+     */
+    void setMetadata(std::shared_ptr<CollectionMetadata> newMetadata);
+
+private:
+    // Namespace to which this state belongs.
+    const NamespaceString _nss;
+
+    // Contains all the chunks associated with this collection. This value is always non-null.
+    std::shared_ptr<CollectionMetadata> _metadata;
+};
+
+}  // namespace mongo