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/**
* Copyright (C) 2022-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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.
*/
#include "mongo/base/error_extra_info.h"
#include "mongo/db/client.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/repl/optime.h"
#include "mongo/db/s/migration_batch_inserter.h"
#include "mongo/db/s/migration_batch_mock_inserter.h"
#include "mongo/db/s/migration_session_id.h"
#include "mongo/db/shard_id.h"
#include "mongo/logv2/log.h"
#include "mongo/s/client/shard.h"
#include "mongo/s/grid.h"
#include "mongo/util/cancellation.h"
#include "mongo/util/concurrency/thread_pool.h"
#include "mongo/util/producer_consumer_queue.h"
#pragma once
namespace mongo {
// This class is only instantiated on the destination of a chunk migration and
// has a single purpose: to manage two thread pools, one
// on which threads perform inserters, and one on which
// threads run _migrateClone requests (to fetch batches of documents to insert).
//
// The constructor creates and starts the inserter thread pool. The destructor shuts down
// and joins the inserter thread pool.
//
// The main work of the class is in method fetchAndScheduleInsertion. That method
// starts a thread pool for fetchers. Each thread in that thread pool sits in a loop
// sending out _migrateClone requests, blocking on the response, and scheduling an
// inserter on the inserter thread pool. This function joins and shuts down the
// fetcher thread pool once all batches have been fetched.
//
// Inserter is templated only to allow a mock inserter to exist.
// There is only one implementation of inserter currently, which is MigrationBatchInserter.
//
// A few things to note:
// - After fetchAndScheduleInsertion returns, insertions are still being executed (although fetches
// are not).
// - Sending out _migrateClone requests in parallel implies the need for synchronization on the
// source. See the comments in migration_chunk_cloner_source.h for details around
// that.
// - The requirement on source side synchronization implies that care must be taken on upgrade.
// In particular, if the source is running an earlier binary that doesn't have code for
// source side synchronization, it is unsafe to send _migrateClone requests in parallel.
// To handle that case, when the source is prepared to service _migrateClone requests in
// parallel, the field "parallelMigrateCloneSupported" is included in the "_recvChunkStart"
// command. The inclusion of that field indicates to the destination that it is safe
// to send _migrateClone requests in parallel. Its exclusion indicates that it is unsafe.
template <typename Inserter>
class MigrationBatchFetcher {
public:
MigrationBatchFetcher(OperationContext* outerOpCtx,
OperationContext* innerOpCtx,
NamespaceString nss,
MigrationSessionId sessionId,
const WriteConcernOptions& writeConcern,
const ShardId& fromShardId,
const ChunkRange& range,
const UUID& migrationId,
const UUID& collectionId,
std::shared_ptr<MigrationCloningProgressSharedState> migrationInfo,
bool parallelFetchingSupported);
~MigrationBatchFetcher();
// Repeatedly fetch batches (using _migrateClone request) and schedule inserter jobs
// on thread pool.
void fetchAndScheduleInsertion();
// Get inserter thread pool stats.
ThreadPool::Stats getThreadPoolStats() const {
return _inserterWorkers->getStats();
}
private:
NamespaceString _nss;
// Size of thread pools.
int _migrationConcurrency;
MigrationSessionId _sessionId;
// Inserter thread pool.
std::unique_ptr<ThreadPool> _inserterWorkers;
BSONObj _migrateCloneRequest;
OperationContext* _outerOpCtx;
OperationContext* _innerOpCtx;
std::shared_ptr<Shard> _fromShard;
// Shared state, by which the progress of migration is communicated
// to MigrationDestinationManager.
std::shared_ptr<MigrationCloningProgressSharedState> _migrationProgress;
ChunkRange _range;
UUID _collectionUuid;
UUID _migrationId;
WriteConcernOptions _writeConcern;
// Indicates if source is prepared to service _migrateClone requests in parallel.
bool _isParallelFetchingSupported;
// Given session id and namespace, create migrateCloneRequest.
// Only should be created once for the lifetime of the object.
BSONObj _createMigrateCloneRequest() const {
BSONObjBuilder builder;
builder.append("_migrateClone", _nss.ns());
_sessionId.append(&builder);
return builder.obj();
}
void _runFetcher();
// Fetches next batch using _migrateClone request and return it. May return an empty batch.
BSONObj _fetchBatch(OperationContext* opCtx);
static bool _isEmptyBatch(const BSONObj& batch) {
return batch.getField("objects").Obj().isEmpty();
}
static void onCreateThread(const std::string& threadName) {
Client::initThread(threadName, getGlobalServiceContext(), nullptr);
{
stdx::lock_guard<Client> lk(cc());
cc().setSystemOperationKillableByStepdown(lk);
}
}
}; // namespace mongo
} // namespace mongo
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