Method writeFile

src/Backups/BackupImpl.cpp:1025–1122

void BackupImpl::writeFile(const BackupFileInfo & info, BackupEntryPtr entry)
{
    /// we don't write anything for reference files
    if (entry->isReference())
        return;

    if (entry->isFromRemoteFile())
    {
        LOG_TRACE(log, "Writing backup for file {} : skipped because of lightweight snapshot", info.data_file_name);
        std::lock_guard lock{mutex};
        original_endpoint = entry->getEndpointURI();
        original_namespace = entry->getNamespace();
        return;
    }

    if (open_mode == OpenMode::READ)
        throw Exception(ErrorCodes::LOGICAL_ERROR, "The backup file should not be opened for reading. Something is wrong internally");

    if (writing_finalized)
        throw Exception(ErrorCodes::LOGICAL_ERROR, "Backup is already finalized");

    {
        std::lock_guard lock{mutex};
        ++num_files;
        total_size += info.size;
    }

    auto src_disk = entry->getDisk();
    auto src_file_path = entry->getFilePath();
    bool from_immutable_file = entry->isFromImmutableFile();
    String src_file_desc = src_file_path.empty() ? "memory buffer" : ("file " + src_file_path);

    if (info.data_file_name.empty())
    {
        LOG_TRACE(log, "Writing backup for file {} from {}: skipped, {}", info.data_file_name, src_file_desc, !info.size ? "empty" : "base backup has it");
        return;
    }

    if (!coordination->startWritingFile(info.data_file_index))
    {
        LOG_TRACE(log, "Writing backup for file {} from {}: skipped, data file #{} is already being written", info.data_file_name, src_file_desc, info.data_file_index);
        return;
    }

    if (!lock_file_before_first_file_checked.exchange(true))
        checkLockFile(true);

    /// NOTE: `mutex` must be unlocked during copying otherwise writing will be in one thread maximum and hence slow.

    const auto write_info_to_archive = [&](const auto & file_name)
    {
        auto out = archive_writer->writeFile(file_name, info.size);
        auto read_buffer = entry->getReadBuffer(writer->getReadSettings());
        if (info.base_size != 0)
            read_buffer->seek(info.base_size, SEEK_SET);
        copyData(*read_buffer, *out);
        out->finalize();
    };