1 2 /** 3 * Copyright (C) 2018-present MongoDB, Inc. 4 * 5 * This program is free software: you can redistribute it and/or modify 6 * it under the terms of the Server Side Public License, version 1, 7 * as published by MongoDB, Inc. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * Server Side Public License for more details. 13 * 14 * You should have received a copy of the Server Side Public License 15 * along with this program. If not, see 16 * <http://www.mongodb.com/licensing/server-side-public-license>. 17 * 18 * As a special exception, the copyright holders give permission to link the 19 * code of portions of this program with the OpenSSL library under certain 20 * conditions as described in each individual source file and distribute 21 * linked combinations including the program with the OpenSSL library. You 22 * must comply with the Server Side Public License in all respects for 23 * all of the code used other than as permitted herein. If you modify file(s) 24 * with this exception, you may extend this exception to your version of the 25 * file(s), but you are not obligated to do so. If you do not wish to do so, 26 * delete this exception statement from your version. If you delete this 27 * exception statement from all source files in the program, then also delete 28 * it in the license file. 29 */ 30 31 #pragma once 32 33 #include "mongo/base/disallow_copying.h" 34 #include "mongo/db/repl/optime.h" 35 #include "mongo/s/client/shard.h" 36 #include "mongo/stdx/mutex.h" 37 38 namespace mongo { 39 40 /** 41 * Implements the support for "read your own write" when run on a node of a replica set. Can be used 42 * in the scenarios where causal consistency is not available yet. 43 */ 44 class RSLocalClient { 45 MONGO_DISALLOW_COPYING(RSLocalClient); 46 47 public: 48 explicit RSLocalClient() = default; 49 50 ~RSLocalClient() = default; 51 52 /** 53 * Runs the specified command returns the BSON command response plus parsed out Status of this 54 * response and write concern error (if present). 55 */ 56 StatusWith<Shard::CommandResponse> runCommandOnce(OperationContext* opCtx, 57 const std::string& dbName, 58 const BSONObj& cmdObj); 59 60 /** 61 * Warning: This method exhausts the cursor and pulls all data into memory. 62 * Do not use other than for very small (i.e., admin or metadata) collections. 63 */ 64 StatusWith<Shard::QueryResponse> queryOnce(OperationContext* opCtx, 65 const ReadPreferenceSetting& readPref, 66 const repl::ReadConcernLevel& readConcernLevel, 67 const NamespaceString& nss, 68 const BSONObj& query, 69 const BSONObj& sort, 70 boost::optional<long long> limit); 71 72 private: 73 /** 74 * Checks if an OpTime was set on the current Client (ie if the current operation performed a 75 * write) and if so updates _lastOpTime to the OpTime from the write that was just performed. 76 * The 'previousOpTimeOnClient' parameter is the optime that *was* the optime on this client 77 * before we ran this command through this RSLocalClient. By the time this method is called, 78 * if the optime set on the Client is different than 'previousOpTimeOnClient' then that means 79 * the command just run did a write and we should update _lastOpTime to capture the optime of 80 * the write we just did. If the current optime on the client is the same as 81 * 'previousOpTimeOnClient' then the command we just ran didn't do a write, and we should leave 82 * _lastOpTime alone. 83 */ 84 void _updateLastOpTimeFromClient(OperationContext* opCtx, 85 const repl::OpTime& previousOpTimeOnClient); 86 87 repl::OpTime _getLastOpTime(); 88 89 // Guards _lastOpTime below. 90 stdx::mutex _mutex; 91 92 // Stores the optime that was generated by the last operation to perform a write that was run 93 // through _runCommand. Used in _exhaustiveFindOnConfig for waiting for that optime to be 94 // committed so that readConcern majority reads will read the writes that were performed without 95 // a w:majority write concern. 96 repl::OpTime _lastOpTime{}; 97 }; 98 99 } // namespace mongo 100