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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 <boost/optional.hpp>
#include <memory>
#include "mongo/base/disallow_copying.h"
#include "mongo/client/dbclientcursor.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/repl/optime.h"
#include "mongo/db/session_txn_record_gen.h"
#include "mongo/db/transaction_history_iterator.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/concurrency/with_lock.h"
namespace mongo {
class OperationContext;
class ScopedSession;
class ServiceContext;
/**
* Provides facilities for extracting oplog entries of writes in a particular namespace that needs
* to be migrated.
*
* This also ensures that oplog returned are majority committed. This is achieved by calling
* waitForWriteConcern. However, waitForWriteConcern does not support waiting for opTimes of
* previous terms. To get around this, the waitForWriteConcern is performed in two phases:
*
* During init() call phase:
* 1. Scan the entire config.transactions and extract all the lastWriteOpTime.
* 2. Insert a no-op oplog entry and wait for it to be majority committed.
* 3. At this point any writes before should be majority committed (including all the oplog
* entries that the collected lastWriteOpTime points to). If the particular oplog with the
* opTime cannot be found: it either means that the oplog was truncated or rolled back.
*
* New writes/xfer mods phase oplog entries:
* In this case, caller is responsible for calling waitForWriteConcern. If getLastFetchedOplog
* returns shouldWaitForMajority == true, it should wait for the highest opTime it has got from
* getLastFetchedOplog. It should also error if it detects a change of term within a batch since
* it would be wrong to wait for the highest opTime in this case.
*/
class SessionCatalogMigrationSource {
MONGO_DISALLOW_COPYING(SessionCatalogMigrationSource);
public:
struct OplogResult {
OplogResult(boost::optional<repl::OplogEntry> _oplog, bool _shouldWaitForMajority)
: oplog(std::move(_oplog)), shouldWaitForMajority(_shouldWaitForMajority) {}
// The oplog fetched.
boost::optional<repl::OplogEntry> oplog;
// If this is set to true, oplog returned is not confirmed to be majority committed,
// so the caller has to explicitly wait for it to be committed to majority.
bool shouldWaitForMajority = false;
};
SessionCatalogMigrationSource(OperationContext* opCtx, NamespaceString ns);
/**
* Returns true if there are more oplog entries to fetch at this moment. Note that new writes
* can still continue to come in after this has returned false, so it can become true again.
* Once this has returned false, this means that it has depleted the existing buffer so it
* is a good time to enter the critical section.
*/
bool hasMoreOplog();
/**
* Attempts to fetch the next oplog entry. Returns true if it was able to fetch anything.
*/
bool fetchNextOplog(OperationContext* opCtx);
/**
* Returns the oplog document that was last fetched by the fetchNextOplog call.
* Returns an empty object if there are no oplog to fetch.
*/
OplogResult getLastFetchedOplog();
/**
* Remembers the oplog timestamp of a new write that just occurred.
*/
void notifyNewWriteOpTime(repl::OpTime opTimestamp);
private:
/**
* An iterator for extracting session write oplogs that need to be cloned during migration.
*/
class SessionOplogIterator {
public:
SessionOplogIterator(SessionTxnRecord txnRecord, int expectedRollbackId);
/**
* Returns true if there are more oplog entries to fetch for this session.
*/
bool hasNext() const;
/**
* Returns the next oplog write that happened in this session. If the oplog is lost
* because the oplog rolled over, this will return a sentinel oplog entry instead with
* type 'n' and o2 field set to Session::kDeadEndSentinel. This will also mean that
* next subsequent calls to hasNext will return false.
*/
repl::OplogEntry getNext(OperationContext* opCtx);
BSONObj toBSON() const {
return _record.toBSON();
}
private:
const SessionTxnRecord _record;
const int _initialRollbackId;
std::unique_ptr<TransactionHistoryIterator> _writeHistoryIterator;
};
///////////////////////////////////////////////////////////////////////////
// Methods for extracting the oplog entries from session information.
/**
* If this returns false, it just means that there are no more oplog entry in the buffer that
* needs to be moved over. However, there can still be new incoming operations that can add
* new entries. Also see hasNewWrites.
*/
bool _hasMoreOplogFromSessionCatalog();
/**
* Attempts to extract the next oplog document by following the oplog chain from the sessions
* catalog. Returns true if a document was actually fetched.
*/
bool _fetchNextOplogFromSessionCatalog(OperationContext* opCtx);
/**
* Returns the document that was last fetched by fetchNextOplogFromSessionCatalog.
*/
repl::OplogEntry _getLastFetchedOplogFromSessionCatalog();
/**
* Extracts oplog information from the current writeHistoryIterator to _lastFetchedOplog. This
* handles insert/update/delete/findAndModify oplog entries.
*
* Returns true if current writeHistoryIterator has any oplog entry.
*/
bool _handleWriteHistory(WithLock, OperationContext* opCtx);
///////////////////////////////////////////////////////////////////////////
// Methods for capturing and extracting oplog entries for new writes.
/**
* Returns true if there are oplog generated by new writes that needs to be fetched.
*/
bool _hasNewWrites();
/**
* Attempts to fetch the next oplog entry from the new writes that was saved by saveNewWriteTS.
* Returns true if there were documents that were retrieved.
*/
bool _fetchNextNewWriteOplog(OperationContext* opCtx);
/**
* Returns the oplog that was last fetched by fetchNextNewWriteOplog.
*/
repl::OplogEntry _getLastFetchedNewWriteOplog();
// Namespace for which the migration is happening
const NamespaceString _ns;
// The rollback id just before migration started. This value is needed so that step-down
// followed by step-up situations can be discovered.
const int _rollbackIdAtInit;
// Protects _sessionCatalogCursor, _sessionOplogIterators, _currentOplogIterator,
// _lastFetchedOplogBuffer, _lastFetchedOplog
stdx::mutex _sessionCloneMutex;
// List of remaining session records that needs to be cloned.
std::vector<std::unique_ptr<SessionOplogIterator>> _sessionOplogIterators;
// Points to the current session record eing cloned.
std::unique_ptr<SessionOplogIterator> _currentOplogIterator;
// Used for temporarily storng oplog entries for operations that has more than one entry.
// For example, findAndModify generates one for the actual operation and another for the
// pre/post image.
std::vector<repl::OplogEntry> _lastFetchedOplogBuffer;
// Used to store the last fetched oplog. This enables calling get multiple times.
boost::optional<repl::OplogEntry> _lastFetchedOplog;
// Protects _newWriteTsList, _lastFetchedNewWriteOplog
stdx::mutex _newOplogMutex;
// Stores oplog opTime of new writes that are coming in.
std::list<repl::OpTime> _newWriteOpTimeList;
// Used to store the last fetched oplog from _newWriteTsList.
boost::optional<repl::OplogEntry> _lastFetchedNewWriteOplog;
};
} // namespace mongo
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