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database_holder_impl.h
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database_holder_impl.h
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/**
* Copyright (C) 2017 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/db/catalog/database_holder.h"
#include <set>
#include <string>
#include "mongo/base/string_data.h"
#include "mongo/db/namespace_string.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/concurrency/mutex.h"
#include "mongo/util/string_map.h"
namespace mongo {
class Database;
class OperationContext;
/**
* Registry of opened databases.
*/
//DatabaseHolderImpl.dbs[]和KVStorageEngine._dbs[]的区别及联系:
//1. DatabaseHolderImpl.dbs[]包含实例启动后使用过或者正在使用的DB信息
//2. KVStorageEngine._dbs[]对应从_mdb_catalog.wt元数据文件加载的所有库及其下面表的元数据信息
//3. mongodb启动后,当通过db.xx.collection对某库的某表操作的时候,会生成一个DatabaseImpl,然后调用
// DatabaseImpl::init()从该库对应KVDatabaseCatalogEntryBase中获取该表元数据信息
//4. KVStorageEngine._dbs[]中存的是全量的元数据信息,而DatabaseHolderImpl.dbs[]中存的是自实例启动后
// 到现在为止,通过db.xx.collection.insert()等使用过的库信息。例如有两个库DB1,DB2,当mongod实例重启后
// 我们只访问了DB1,则KVStorageEngine._dbs[]包含有DB1和DB2两个库信息,而DatabaseHolderImpl.dbs[]只包含DB1信息
//AutoGetDb::AutoGetDb或者AutoGetOrCreateDb::AutoGetOrCreateDb->DatabaseHolderImpl::get从DatabaseHolderImpl._dbs数组查找获取Database
//DatabaseImpl::createCollection创建collection的表全部添加到DatabaseImpl._collections数组中
//AutoGetCollection::AutoGetCollection通过Database::getCollection或者UUIDCatalog::lookupCollectionByUUID(从UUIDCatalog._catalog数组通过查找uuid可以获取collection表信息)
//注意AutoGetCollection::AutoGetCollection构造函数可以是uuid,也有一个构造函数是nss,也就是可以通过uuid查找,也可以通过nss查找
class DatabaseHolderImpl : public DatabaseHolder::Impl {
public:
DatabaseHolderImpl() = default;
/**
* Retrieves an already opened database or returns NULL. Must be called with the database
* locked in at least IS-mode.
*/
Database* get(OperationContext* opCtx, StringData ns) const override;
/**
* Retrieves a database reference if it is already opened, or opens it if it hasn't been
* opened/created yet. Must be called with the database locked in X-mode.
*
* @param justCreated Returns whether the database was newly created (true) or it already
* existed (false). Can be NULL if this information is not necessary.
*/
Database* openDb(OperationContext* opCtx, StringData ns, bool* justCreated = nullptr) override;
/**
* Closes the specified database. Must be called with the database locked in X-mode.
*/
void close(OperationContext* opCtx, StringData ns, const std::string& reason) override;
/**
* Closes all opened databases. Must be called with the global lock acquired in X-mode.
*
* @param result Populated with the names of the databases, which were closed.
* @param force Force close even if something underway - use at shutdown
* @param reason The reason for close.
*/
bool closeAll(OperationContext* opCtx,
BSONObjBuilder& result,
bool force,
const std::string& reason) override;
/**
* Returns the set of existing database names that differ only in casing.
*/
std::set<std::string> getNamesWithConflictingCasing(StringData name) override;
private:
std::set<std::string> _getNamesWithConflictingCasing_inlock(StringData name);
//对应DatabaseImpl
typedef StringMap<Database*> DBs;
mutable SimpleMutex _m;
//AutoGetDb::AutoGetDb或者AutoGetOrCreateDb::AutoGetOrCreateDb->DatabaseHolderImpl::get从DatabaseHolderImpl._dbs数组查找获取Database
//DatabaseImpl::createCollection创建collection的表全部添加到DatabaseImpl._collections数组中
//AutoGetCollection::AutoGetCollection通过Database::getCollection或者UUIDCatalog::lookupCollectionByUUID(从UUIDCatalog._catalog数组通过查找uuid可以获取collection表信息)
//注意AutoGetCollection::AutoGetCollection构造函数可以是uuid,也有一个构造函数是nss,也就是可以通过uuid查找,也可以通过nss查找
//DatabaseHolderImpl.dbs[]和KVStorageEngine._dbs[]的区别及联系:
//1. DatabaseHolderImpl.dbs[]包含实例启动后使用过或者正在使用的DB信息
//2. KVStorageEngine._dbs[]对应从_mdb_catalog.wt元数据文件加载的所有库及其下面表的元数据信息
//3. mongodb启动后,当通过db.xx.collection对某库的某表操作的时候,会生成一个DatabaseImpl,然后调用
// DatabaseImpl::init()从该库对应KVDatabaseCatalogEntryBase中获取该表元数据信息
//4. KVStorageEngine._dbs[]中存的是全量的元数据信息,而DatabaseHolderImpl.dbs[]中存的是自实例启动后
// 到现在为止,通过db.xx.collection.insert()等使用过的库信息。例如有两个库DB1,DB2,当mongod实例重启后
// 我们只访问了DB1,则KVStorageEngine._dbs[]包含有DB1和DB2两个库信息,而DatabaseHolderImpl.dbs[]只包含DB1信息
//保存到database_holder_impl.h中的全局变量_dbHolder
//所有db保存到这里,通过DatabaseHolderImpl::openDb创建后保存到这里
DBs _dbs;
};
} // namespace mongo