**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.
}
    return res;
}
DetachedPartsInfo MergeTreeData::getDetachedParts() const
{
    DetachedPartsInfo res;
    for (const auto & disk : getDisks())
    {
        String detached_path = fs::path(relative_data_path) / MergeTreeData::DETACHED_DIR_NAME;
        /
        if (disk->exists(detached_path))
        {
            for (auto it = disk->iterateDirectory(detached_path); it->isValid(); it->next())
            {
                res.push_back(DetachedPartInfo::parseDetachedPartName(disk, it->name(), format_version));
            }
        }
    }
    return res;
}
void MergeTreeData::validateDetachedPartName(const String & name)
{
    if (name.find('/') != std::string::npos || name == "." || name == "..")
        throw DB::Exception("Invalid part name '" + name + "'", ErrorCodes::INCORRECT_FILE_NAME);
    if (startsWith(name, "attaching_") || startsWith(name, "deleting_"))
        throw DB::Exception("Cannot drop part " + name + ": "
                            "most likely it is used by another DROP or ATTACH query.",
                            ErrorCodes::BAD_DATA_PART_NAME);
}
void MergeTreeData::dropDetached(const ASTPtr & partition, bool part, ContextPtr local_context)