```
ubuntu@ip-172-31-79-147:/opt/downloads$ clickhouse-local --max_threads 8 --query "WITH parseDateTimeBestEffort(extract(_path, 'pageviews-([\\d\\-]+)\\.gz$')) AS time, splitByChar(' ', line) AS values, splitByChar('.', values[1]) AS projects SELECT time, projects[1] AS project, projects[2] AS subproject, values[2] AS path, (values[3])::UInt64 AS hits FROM file('pageviews*.gz', LineAsString) WHERE length(values) >= 3" | pv > /dev/null
^C01GiB 0:01:08 [ 129MiB/s] [                                                                                                                                                                   <=>                                                                                    ]

ubuntu@ip-172-31-79-147:/opt/downloads$ clickhouse-local --max_threads 8 --query "WITH parseDateTimeBestEffort(extract(toLowCardinality(_path), 'pageviews-([\\d\\-]+)\\.gz$')) AS time, splitByChar(' ', line) AS values, splitByChar('.', values[1]) AS projects SELECT time, projects[1] AS project, projects[2] AS subproject, values[2] AS path, (values[3])::UInt64 AS hits FROM file('pageviews*.gz', LineAsString) WHERE length(values) >= 3" | pv > /dev/null
^C46GiB 0:00:48 [ 175MiB/s] [                                                                                                                                                                                                                                        <=>               ]
```

{
        std::lock_guard lock(mutex);
        if (uris_iter == uris.end())
            return "";
        auto key = *uris_iter;
        ++uris_iter;
        return key;
    }
private:
    std::mutex mutex;
    Strings uris;
    Strings::iterator uris_iter;
};
Block HDFSSource::getHeader(const StorageMetadataPtr & metadata_snapshot, bool need_path_column, bool need_file_column)
{
    auto header = metadata_snapshot->getSampleBlock();
    
    if (need_path_column)
        header.insert({DataTypeString().createColumn(), std::make_shared<DataTypeString>(), "_path"});
    if (need_file_column)
        header.insert({DataTypeString().createColumn(), std::make_shared<DataTypeString>(), "_file"});
    return header;
}
Block HDFSSource::getBlockForSource(