**How to reproduce**
Clickhouse server 20.13.1.5273
```
CREATE TABLE default.test
(
`key` UInt32,
`ts` DateTime CODEC(DoubleDelta, LZ4),
`db_time` DateTime DEFAULT now() COMMENT 'spout-ignore' CODEC(DoubleDelta, LZ4)
)
ENGINE = MergeTree
PARTITION BY toStartOfTenMinutes(db_time)
ORDER BY (key, ts)
TTL db_time + toIntervalHour(3)
SETTINGS index_granularity = 8192, merge_with_ttl_timeout = 3600, min_rows_for_compact_part = 1000000, min_bytes_for_compact_part = 200000000, in_memory_parts_enable_wal = 0;


INSERT INTO test(key, ts) SELECT number % 1000, now() + intDiv(number,1000) FROM numbers(500);

SELECT * FROM test;
500 rows in set. Elapsed: 0.003 sec.

DETACH TABLE test;

ATTACH TABLE test;

SELECT * FROM test;

0 rows in set. Elapsed: 0.002 sec.
```

**Expected behavior**
Clickhouse would flush parts on disk.
}
    }
    setDataVolume(0, 0, 0);
    LOG_TRACE(log, "dropAllData: done.");
}
void MergeTreeData::dropIfEmpty()
{
    LOG_TRACE(log, "dropIfEmpty");
    auto lock = lockParts();
    if (!data_parts_by_info.empty())
        return;
    try
    {
        for (const auto & disk : getDisks())
        {
            
            disk->removeFileIfExists(fs::path(relative_data_path) / MergeTreeData::FORMAT_VERSION_FILE_NAME);
            disk->removeDirectory(fs::path(relative_data_path) / MergeTreeData::DETACHED_DIR_NAME);
            disk->removeDirectory(relative_data_path);
        }
    }
    catch (...)
    {
        
        tryLogCurrentException(__PRETTY_FUNCTION__);
    }
}
namespace
{
bool isSafeForKeyConversion(const IDataType * from, const IDataType * to)