Status Balancer::rebalanceSingleChunk(OperationContext* txn, const ChunkType& chunk) {
auto migrateStatus = _chunkSelectionPolicy->selectSpecificChunkToMove(txn, chunk);
if (!migrateStatus.isOK()) {
return migrateStatus.getStatus();
}
auto migrateInfo = std::move(migrateStatus.getValue());
if (!migrateInfo) {
LOG(1) << "Unable to find more appropriate location for chunk " << redact(chunk.toString());
return Status::OK();
}
auto balancerConfig = Grid::get(txn)->getBalancerConfiguration();
Status refreshStatus = balancerConfig->refreshAndCheck(txn);
if (!refreshStatus.isOK()) {
return refreshStatus;
}
MigrationManager migrationManager;
auto migrationStatuses = migrationManager.scheduleMigrations(
txn,
{MigrationManager::MigrationRequest(std::move(*migrateInfo),
balancerConfig->getMaxChunkSizeBytes(),
balancerConfig->getSecondaryThrottle(),
balancerConfig->waitForDelete())});
invariant(migrationStatuses.size() == 1);
auto scopedCMStatus = ScopedChunkManager::getExisting(txn, NamespaceString(chunk.getNS()));
if (!scopedCMStatus.isOK()) {
return scopedCMStatus.getStatus();
}
auto scopedCM = std::move(scopedCMStatus.getValue());
ChunkManager* const cm = scopedCM.cm();
cm->reload(txn);
return migrationStatuses.begin()->second;
}
