void ChunkManagerTargeter::noteStaleResponse(const ShardEndpoint& endpoint, const StaleConfigInfo& staleInfo) { dassert(!_needsTargetingRefresh); ChunkVersion remoteShardVersion; if (!staleInfo.getVersionWanted()) { // If we don't have a vWanted sent, assume the version is higher than our current version. remoteShardVersion = getShardVersion(*_routingInfo, endpoint.shardName); remoteShardVersion.incMajor(); } else { remoteShardVersion = *staleInfo.getVersionWanted(); } ShardVersionMap::iterator it = _remoteShardVersions.find(endpoint.shardName); if (it == _remoteShardVersions.end()) { _remoteShardVersions.insert(std::make_pair(endpoint.shardName, remoteShardVersion)); } else { ChunkVersion& previouslyNotedVersion = it->second; if (previouslyNotedVersion.epoch() == remoteShardVersion.epoch()) { if (previouslyNotedVersion.isOlderThan(remoteShardVersion)) { previouslyNotedVersion = remoteShardVersion; } } else { // Epoch changed midway while applying the batch so set the version to something // unique // and non-existent to force a reload when refreshIsNeeded is called. previouslyNotedVersion = ChunkVersion::IGNORED(); } } }
void ChunkManagerTargeter::noteStaleResponse( const ShardEndpoint& endpoint, const BSONObj& staleInfo ) { dassert( !_needsTargetingRefresh ); ChunkVersion remoteShardVersion; if ( staleInfo["vWanted"].eoo() ) { // If we don't have a vWanted sent, assume the version is higher than our current // version. remoteShardVersion = getShardVersion( endpoint.shardName, _manager, _primary ); remoteShardVersion.incMajor(); } else { remoteShardVersion = ChunkVersion::fromBSON( staleInfo, "vWanted" ); } ShardVersionMap::iterator it = _remoteShardVersions.find( endpoint.shardName ); if ( it == _remoteShardVersions.end() ) { _remoteShardVersions.insert( make_pair( endpoint.shardName, remoteShardVersion ) ); } else { ChunkVersion& previouslyNotedVersion = it->second; if ( previouslyNotedVersion.hasCompatibleEpoch( remoteShardVersion )) { if ( previouslyNotedVersion.isOlderThan( remoteShardVersion )) { remoteShardVersion.cloneTo( &previouslyNotedVersion ); } } else { // Epoch changed midway while applying the batch so set the version to // something unique and non-existent to force a reload when // refreshIsNeeded is called. ChunkVersion::IGNORED().cloneTo( &previouslyNotedVersion ); } } }
void ChunkManager::createFirstChunks(OperationContext* txn, const ShardId& primaryShardId, const vector<BSONObj>* initPoints, const set<ShardId>* initShardIds) { // TODO distlock? // TODO: Race condition if we shard the collection and insert data while we split across // the non-primary shard. vector<BSONObj> splitPoints; vector<ShardId> shardIds; calcInitSplitsAndShards(txn, primaryShardId, initPoints, initShardIds, &splitPoints, &shardIds); // this is the first chunk; start the versioning from scratch ChunkVersion version; version.incEpoch(); version.incMajor(); log() << "going to create " << splitPoints.size() + 1 << " chunk(s) for: " << _ns << " using new epoch " << version.epoch(); for (unsigned i = 0; i <= splitPoints.size(); i++) { BSONObj min = i == 0 ? _keyPattern.getKeyPattern().globalMin() : splitPoints[i - 1]; BSONObj max = i < splitPoints.size() ? splitPoints[i] : _keyPattern.getKeyPattern().globalMax(); Chunk temp(this, min, max, shardIds[i % shardIds.size()], version); BSONObjBuilder chunkBuilder; temp.serialize(chunkBuilder); BSONObj chunkObj = chunkBuilder.obj(); Status result = grid.catalogManager(txn)->update(txn, ChunkType::ConfigNS, BSON(ChunkType::name(temp.genID())), chunkObj, true, false, NULL); version.incMinor(); if (!result.isOK()) { string ss = str::stream() << "creating first chunks failed. result: " << result.reason(); error() << ss; msgasserted(15903, ss); } } _version = ChunkVersion(0, 0, version.epoch()); }
void ChunkManagerTargeter::noteStaleResponse( const ShardEndpoint& endpoint, const BSONObj& staleInfo ) { dassert( !_needsTargetingRefresh ); ChunkVersion remoteShardVersion; if ( staleInfo["vWanted"].eoo() ) { // If we don't have a vWanted sent, assume the version is higher than our current // version. remoteShardVersion = getShardVersion( endpoint.shardName, _manager, _primary ); remoteShardVersion.incMajor(); } else { remoteShardVersion = ChunkVersion::fromBSON( staleInfo, "vWanted" ); } // We assume here that we can't have more than one stale config per-shard dassert( _remoteShardVersions.find( endpoint.shardName ) == _remoteShardVersions.end() ); _remoteShardVersions.insert( make_pair( endpoint.shardName, remoteShardVersion ) ); }
/** * Stores ranges for a particular collection and shard starting from some version */ void storeCollectionRanges( const NamespaceString& nss, const string& shardName, const vector<KeyRange>& ranges, const ChunkVersion& startVersion ) { // Get key pattern from first range ASSERT_GREATER_THAN( ranges.size(), 0u ); CollectionType coll; coll.setNS( nss.ns() ); coll.setKeyPattern( ranges.begin()->keyPattern ); coll.setEpoch( startVersion.epoch() ); coll.setUpdatedAt( 1ULL ); string errMsg; ASSERT( coll.isValid( &errMsg ) ); DBDirectClient client(&_txn); client.update( CollectionType::ConfigNS, BSON( CollectionType::ns( coll.getNS() ) ), coll.toBSON(), true, false ); ChunkVersion nextVersion = startVersion; for ( vector<KeyRange>::const_iterator it = ranges.begin(); it != ranges.end(); ++it ) { ChunkType chunk; // TODO: We should not rely on the serialized ns, minkey being unique in the future, // causes problems since it links string serialization to correctness. chunk.setName( Chunk::genID( nss, it->minKey ) ); chunk.setShard( shardName ); chunk.setNS( nss.ns() ); chunk.setVersion( nextVersion ); chunk.setMin( it->minKey ); chunk.setMax( it->maxKey ); nextVersion.incMajor(); client.insert( ChunkType::ConfigNS, chunk.toBSON() ); } }
Status ChunkMoveOperationState::commitMigration() { invariant(_distLockStatus.is_initialized()); invariant(_distLockStatus->isOK()); log() << "About to enter migrate critical section"; // We're under the collection distributed lock here, so no other migrate can change maxVersion // or CollectionMetadata state. ShardingState* const shardingState = ShardingState::get(_txn); Status startStatus = ShardingStateRecovery::startMetadataOp(_txn); if (!startStatus.isOK()) return startStatus; shardingState->migrationSourceManager()->setInCriticalSection(true); const ChunkVersion originalCollVersion = getCollMetadata()->getCollVersion(); ChunkVersion myVersion = originalCollVersion; myVersion.incMajor(); { ScopedTransaction transaction(_txn, MODE_IX); Lock::DBLock lk(_txn->lockState(), _nss.db(), MODE_IX); Lock::CollectionLock collLock(_txn->lockState(), _nss.ns(), MODE_X); invariant(myVersion > shardingState->getVersion(_nss.ns())); // Bump the metadata's version up and "forget" about the chunk being moved. This is // not the commit point, but in practice the state in this shard won't change until // the commit it done. shardingState->donateChunk(_txn, _nss.ns(), _minKey, _maxKey, myVersion); } log() << "moveChunk setting version to: " << myVersion << migrateLog; // We're under the collection lock here, too, so we can undo the chunk donation because // no other state change could be ongoing BSONObj res; Status recvChunkCommitStatus{ErrorCodes::InternalError, "status not set"}; try { ScopedDbConnection connTo(_toShardCS, 35.0); connTo->runCommand("admin", BSON("_recvChunkCommit" << 1), res); connTo.done(); recvChunkCommitStatus = getStatusFromCommandResult(res); } catch (const DBException& e) { const string msg = stream() << "moveChunk could not contact to shard " << _toShard << " to commit transfer" << causedBy(e); warning() << msg; recvChunkCommitStatus = Status(e.toStatus().code(), msg); } if (MONGO_FAIL_POINT(failMigrationCommit) && recvChunkCommitStatus.isOK()) { recvChunkCommitStatus = Status(ErrorCodes::InternalError, "Failing _recvChunkCommit due to failpoint."); } if (!recvChunkCommitStatus.isOK()) { log() << "moveChunk migrate commit not accepted by TO-shard: " << res << " resetting shard version to: " << getShardVersion() << migrateLog; { ScopedTransaction transaction(_txn, MODE_IX); Lock::DBLock dbLock(_txn->lockState(), _nss.db(), MODE_IX); Lock::CollectionLock collLock(_txn->lockState(), _nss.ns(), MODE_X); log() << "moveChunk collection lock acquired to reset shard version from " "failed migration"; // Revert the chunk manager back to the state before "forgetting" about the chunk shardingState->undoDonateChunk(_txn, _nss.ns(), getCollMetadata()); } log() << "Shard version successfully reset to clean up failed migration"; return Status(recvChunkCommitStatus.code(), stream() << "_recvChunkCommit failed: " << causedBy(recvChunkCommitStatus)); } log() << "moveChunk migrate commit accepted by TO-shard: " << res << migrateLog; BSONArrayBuilder updates; { // Update for the chunk being moved BSONObjBuilder op; op.append("op", "u"); op.appendBool("b", false); // No upserting op.append("ns", ChunkType::ConfigNS); BSONObjBuilder n(op.subobjStart("o")); n.append(ChunkType::name(), Chunk::genID(_nss.ns(), _minKey)); myVersion.addToBSON(n, ChunkType::DEPRECATED_lastmod()); n.append(ChunkType::ns(), _nss.ns()); n.append(ChunkType::min(), _minKey); n.append(ChunkType::max(), _maxKey); n.append(ChunkType::shard(), _toShard); n.done(); BSONObjBuilder q(op.subobjStart("o2")); q.append(ChunkType::name(), Chunk::genID(_nss.ns(), _minKey)); q.done(); updates.append(op.obj()); } // Version at which the next highest lastmod will be set. If the chunk being moved is the last // in the shard, nextVersion is that chunk's lastmod otherwise the highest version is from the // chunk being bumped on the FROM-shard. ChunkVersion nextVersion = myVersion; // If we have chunks left on the FROM shard, update the version of one of them as well. We can // figure that out by grabbing the metadata as it has been changed. const std::shared_ptr<CollectionMetadata> bumpedCollMetadata( shardingState->getCollectionMetadata(_nss.ns())); if (bumpedCollMetadata->getNumChunks() > 0) { // get another chunk on that shard ChunkType bumpChunk; invariant(bumpedCollMetadata->getNextChunk(bumpedCollMetadata->getMinKey(), &bumpChunk)); BSONObj bumpMin = bumpChunk.getMin(); BSONObj bumpMax = bumpChunk.getMax(); dassert(bumpMin.woCompare(_minKey) != 0); BSONObjBuilder op; op.append("op", "u"); op.appendBool("b", false); op.append("ns", ChunkType::ConfigNS); nextVersion.incMinor(); // same as used on donateChunk BSONObjBuilder n(op.subobjStart("o")); n.append(ChunkType::name(), Chunk::genID(_nss.ns(), bumpMin)); nextVersion.addToBSON(n, ChunkType::DEPRECATED_lastmod()); n.append(ChunkType::ns(), _nss.ns()); n.append(ChunkType::min(), bumpMin); n.append(ChunkType::max(), bumpMax); n.append(ChunkType::shard(), _fromShard); n.done(); BSONObjBuilder q(op.subobjStart("o2")); q.append(ChunkType::name(), Chunk::genID(_nss.ns(), bumpMin)); q.done(); updates.append(op.obj()); log() << "moveChunk updating self version to: " << nextVersion << " through " << bumpMin << " -> " << bumpMax << " for collection '" << _nss.ns() << "'" << migrateLog; } else { log() << "moveChunk moved last chunk out for collection '" << _nss.ns() << "'" << migrateLog; } BSONArrayBuilder preCond; { BSONObjBuilder b; b.append("ns", ChunkType::ConfigNS); b.append("q", BSON("query" << BSON(ChunkType::ns(_nss.ns())) << "orderby" << BSON(ChunkType::DEPRECATED_lastmod() << -1))); { BSONObjBuilder bb(b.subobjStart("res")); // TODO: For backwards compatibility, we can't yet require an epoch here bb.appendTimestamp(ChunkType::DEPRECATED_lastmod(), originalCollVersion.toLong()); bb.done(); } preCond.append(b.obj()); } Status applyOpsStatus{Status::OK()}; try { // For testing migration failures if (MONGO_FAIL_POINT(failMigrationConfigWritePrepare)) { throw DBException("mock migration failure before config write", ErrorCodes::PrepareConfigsFailed); } applyOpsStatus = grid.catalogManager(_txn)->applyChunkOpsDeprecated(_txn, updates.arr(), preCond.arr()); if (MONGO_FAIL_POINT(failMigrationApplyOps)) { throw SocketException(SocketException::RECV_ERROR, shardingState->getConfigServer(_txn).toString()); } } catch (const DBException& ex) { warning() << ex << migrateLog; applyOpsStatus = ex.toStatus(); } if (applyOpsStatus == ErrorCodes::PrepareConfigsFailed) { // In the process of issuing the migrate commit, the SyncClusterConnection checks that // the config servers are reachable. If they are not, we are sure that the applyOps // command was not sent to any of the configs, so we can safely back out of the // migration here, by resetting the shard version that we bumped up to in the // donateChunk() call above. log() << "About to acquire moveChunk coll lock to reset shard version from " << "failed migration"; { ScopedTransaction transaction(_txn, MODE_IX); Lock::DBLock dbLock(_txn->lockState(), _nss.db(), MODE_IX); Lock::CollectionLock collLock(_txn->lockState(), _nss.ns(), MODE_X); // Revert the metadata back to the state before "forgetting" about the chunk shardingState->undoDonateChunk(_txn, _nss.ns(), getCollMetadata()); } log() << "Shard version successfully reset to clean up failed migration"; const string msg = stream() << "Failed to send migrate commit to configs " << causedBy(applyOpsStatus); return Status(applyOpsStatus.code(), msg); } else if (!applyOpsStatus.isOK()) { // This could be a blip in the connectivity. Wait out a few seconds and check if the // commit request made it. // // If the commit made it to the config, we'll see the chunk in the new shard and // there's no further action to be done. // // If the commit did not make it, currently the only way to fix this state is to // bounce the mongod so that the old state (before migrating) is brought in. warning() << "moveChunk commit outcome ongoing" << migrateLog; sleepsecs(10); // Look for the chunk in this shard whose version got bumped. We assume that if that // mod made it to the config server, then applyOps was successful. try { std::vector<ChunkType> newestChunk; Status status = grid.catalogManager(_txn)->getChunks(_txn, BSON(ChunkType::ns(_nss.ns())), BSON(ChunkType::DEPRECATED_lastmod() << -1), 1, &newestChunk, nullptr); uassertStatusOK(status); ChunkVersion checkVersion; if (!newestChunk.empty()) { invariant(newestChunk.size() == 1); checkVersion = newestChunk[0].getVersion(); } if (checkVersion.equals(nextVersion)) { log() << "moveChunk commit confirmed" << migrateLog; } else { error() << "moveChunk commit failed: version is at " << checkVersion << " instead of " << nextVersion << migrateLog; error() << "TERMINATING" << migrateLog; dbexit(EXIT_SHARDING_ERROR); } } catch (...) { error() << "moveChunk failed to get confirmation of commit" << migrateLog; error() << "TERMINATING" << migrateLog; dbexit(EXIT_SHARDING_ERROR); } } MONGO_FAIL_POINT_PAUSE_WHILE_SET(hangBeforeLeavingCriticalSection); shardingState->migrationSourceManager()->setInCriticalSection(false); ShardingStateRecovery::endMetadataOp(_txn); // Migration is done, just log some diagnostics information BSONObj chunkInfo = BSON("min" << _minKey << "max" << _maxKey << "from" << _fromShard << "to" << _toShard); BSONObjBuilder commitInfo; commitInfo.appendElements(chunkInfo); if (res["counts"].type() == Object) { commitInfo.appendElements(res["counts"].Obj()); } grid.catalogManager(_txn)->logChange(_txn, "moveChunk.commit", _nss.ns(), commitInfo.obj()); shardingState->migrationSourceManager()->done(_txn); _isRunning = false; return Status::OK(); }
Status MigrationSourceManager::commitDonateChunk(OperationContext* txn) { invariant(!txn->lockState()->isLocked()); invariant(_state == kCriticalSection); auto scopedGuard = MakeGuard([&] { cleanupOnError(txn); }); // Tell the recipient shard to fetch the latest changes Status commitCloneStatus = _cloneDriver->commitClone(txn); if (MONGO_FAIL_POINT(failMigrationCommit) && commitCloneStatus.isOK()) { commitCloneStatus = {ErrorCodes::InternalError, "Failing _recvChunkCommit due to failpoint."}; } if (!commitCloneStatus.isOK()) { return {commitCloneStatus.code(), str::stream() << "commit clone failed due to " << commitCloneStatus.toString()}; } // Generate the next collection version. ChunkVersion uncommittedCollVersion = _committedMetadata->getCollVersion(); uncommittedCollVersion.incMajor(); // applyOps preparation for reflecting the uncommitted metadata on the config server // Preconditions BSONArrayBuilder preCond; { BSONObjBuilder b; b.append("ns", ChunkType::ConfigNS); b.append("q", BSON("query" << BSON(ChunkType::ns(_args.getNss().ns())) << "orderby" << BSON(ChunkType::DEPRECATED_lastmod() << -1))); { BSONObjBuilder bb(b.subobjStart("res")); // TODO: For backwards compatibility, we can't yet require an epoch here bb.appendTimestamp(ChunkType::DEPRECATED_lastmod(), _committedMetadata->getCollVersion().toLong()); bb.done(); } preCond.append(b.obj()); } // Update for the chunk which is being donated BSONArrayBuilder updates; { BSONObjBuilder op; op.append("op", "u"); op.appendBool("b", false); // No upserting op.append("ns", ChunkType::ConfigNS); BSONObjBuilder n(op.subobjStart("o")); n.append(ChunkType::name(), ChunkType::genID(_args.getNss().ns(), _args.getMinKey())); uncommittedCollVersion.addToBSON(n, ChunkType::DEPRECATED_lastmod()); n.append(ChunkType::ns(), _args.getNss().ns()); n.append(ChunkType::min(), _args.getMinKey()); n.append(ChunkType::max(), _args.getMaxKey()); n.append(ChunkType::shard(), _args.getToShardId()); n.done(); BSONObjBuilder q(op.subobjStart("o2")); q.append(ChunkType::name(), ChunkType::genID(_args.getNss().ns(), _args.getMinKey())); q.done(); updates.append(op.obj()); } // Update for the chunk being moved // Version at which the next highest lastmod will be set. If the chunk being moved is the last // in the shard, nextVersion is that chunk's lastmod otherwise the highest version is from the // chunk being bumped on the FROM-shard. ChunkVersion nextVersion = uncommittedCollVersion; // If we have chunks left on the FROM shard, update the version of one of them as well. We can // figure that out by grabbing the metadata as it has been changed. if (_committedMetadata->getNumChunks() > 1) { ChunkType bumpChunk; invariant(_committedMetadata->getDifferentChunk(_args.getMinKey(), &bumpChunk)); BSONObj bumpMin = bumpChunk.getMin(); BSONObj bumpMax = bumpChunk.getMax(); nextVersion.incMinor(); dassert(bumpMin.woCompare(_args.getMinKey()) != 0); BSONObjBuilder op; op.append("op", "u"); op.appendBool("b", false); op.append("ns", ChunkType::ConfigNS); BSONObjBuilder n(op.subobjStart("o")); n.append(ChunkType::name(), ChunkType::genID(_args.getNss().ns(), bumpMin)); nextVersion.addToBSON(n, ChunkType::DEPRECATED_lastmod()); n.append(ChunkType::ns(), _args.getNss().ns()); n.append(ChunkType::min(), bumpMin); n.append(ChunkType::max(), bumpMax); n.append(ChunkType::shard(), _args.getFromShardId()); n.done(); BSONObjBuilder q(op.subobjStart("o2")); q.append(ChunkType::name(), ChunkType::genID(_args.getNss().ns(), bumpMin)); q.done(); updates.append(op.obj()); log() << "moveChunk updating self version to: " << nextVersion << " through " << bumpMin << " -> " << bumpMax << " for collection '" << _args.getNss().ns() << "'"; } else { log() << "moveChunk moved last chunk out for collection '" << _args.getNss().ns() << "'"; } MONGO_FAIL_POINT_PAUSE_WHILE_SET(hangBeforeCommitMigration); Status applyOpsStatus = grid.catalogClient(txn)->applyChunkOpsDeprecated( txn, updates.arr(), preCond.arr(), _args.getNss().ns(), nextVersion); if (MONGO_FAIL_POINT(failCommitMigrationCommand)) { applyOpsStatus = Status(ErrorCodes::InternalError, "Failpoint 'failCommitMigrationCommand' generated error"); } if (applyOpsStatus.isOK()) { // Now that applyOps succeeded and the new collection version is committed, update the // collection metadata to the new collection version and forget the migrated chunk. ScopedTransaction scopedXact(txn, MODE_IX); AutoGetCollection autoColl(txn, _args.getNss(), MODE_IX, MODE_X); ChunkType migratingChunkToForget; migratingChunkToForget.setMin(_args.getMinKey()); migratingChunkToForget.setMax(_args.getMaxKey()); _committedMetadata = _committedMetadata->cloneMigrate(migratingChunkToForget, uncommittedCollVersion); auto css = CollectionShardingState::get(txn, _args.getNss().ns()); css->setMetadata(_committedMetadata); } else { // This could be an unrelated error (e.g. network error). Check whether the metadata update // succeeded by refreshing the collection metadata from the config server and checking that // the original chunks no longer exist. warning() << "Migration metadata commit may have failed: refreshing metadata to check" << causedBy(applyOpsStatus); // Need to get the latest optime in case the refresh request goes to a secondary -- // otherwise the read won't wait for the write that applyChunkOpsDeprecated may have done. Status status = grid.catalogClient(txn)->logChange( txn, "moveChunk.validating", _args.getNss().ns(), BSON("min" << _args.getMinKey() << "max" << _args.getMaxKey() << "from" << _args.getFromShardId() << "to" << _args.getToShardId())); if (!status.isOK()) { fassertStatusOK( 40137, {status.code(), str::stream() << "applyOps failed to commit chunk [" << _args.getMinKey() << "," << _args.getMaxKey() << ") due to " << causedBy(applyOpsStatus) << ", and updating the optime with a write before refreshing the " << "metadata also failed: " << causedBy(status)}); } ShardingState* const shardingState = ShardingState::get(txn); ChunkVersion shardVersion; Status refreshStatus = shardingState->refreshMetadataNow(txn, _args.getNss().ns(), &shardVersion); fassertStatusOK(34431, {refreshStatus.code(), str::stream() << "applyOps failed to commit chunk [" << _args.getMinKey() << "," << _args.getMaxKey() << ") due to " << causedBy(applyOpsStatus) << ", and refreshing collection metadata failed: " << causedBy(refreshStatus)}); { ScopedTransaction scopedXact(txn, MODE_IS); AutoGetCollection autoColl(txn, _args.getNss(), MODE_IS); auto css = CollectionShardingState::get(txn, _args.getNss()); std::shared_ptr<CollectionMetadata> refreshedMetadata = css->getMetadata(); if (refreshedMetadata->keyBelongsToMe(_args.getMinKey())) { invariant(refreshedMetadata->getCollVersion() == _committedMetadata->getCollVersion()); // After refresh, the collection metadata indicates that the donor shard still owns // the chunk, so no migration changes were written to the config server metadata. return {applyOpsStatus.code(), str::stream() << "Migration was not committed, applyOps failed: " << causedBy(applyOpsStatus)}; } ChunkVersion refreshedCollectionVersion = refreshedMetadata->getCollVersion(); if (!refreshedCollectionVersion.equals(nextVersion)) { // The refreshed collection metadata's collection version does not match the control // chunk's updated collection version, which should now be the highest. The control // chunk was not committed, but the migrated chunk was. This state is not // recoverable. fassertStatusOK(40138, {applyOpsStatus.code(), str::stream() << "Migration was partially committed, state is " << "unrecoverable. applyOps error: " << causedBy(applyOpsStatus)}); } } } MONGO_FAIL_POINT_PAUSE_WHILE_SET(hangBeforeLeavingCriticalSection); scopedGuard.Dismiss(); _cleanup(txn); grid.catalogClient(txn)->logChange(txn, "moveChunk.commit", _args.getNss().ns(), BSON("min" << _args.getMinKey() << "max" << _args.getMaxKey() << "from" << _args.getFromShardId() << "to" << _args.getToShardId())); return Status::OK(); }