**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.
current_command_results = unfreezePartition(command.partition, command.with_name, query_context, lock);
            }
            break;
            case PartitionCommand::UNFREEZE_ALL_PARTITIONS:
            {
                auto lock = lockForShare(query_context->getCurrentQueryId(), query_context->getSettingsRef().lock_acquire_timeout);
                current_command_results = unfreezeAll(command.with_name, query_context, lock);
            }
            break;
            default:
                throw Exception("Uninitialized partition command", ErrorCodes::LOGICAL_ERROR);
        }
        for (auto & command_result : current_command_results)
            command_result.command_type = command.typeToString();
        result.insert(result.end(), current_command_results.begin(), current_command_results.end());
    }
    if (query_context->getSettingsRef().alter_partition_verbose_result)
        return convertCommandsResultToSource(result);
    return {};
}
BackupEntries MergeTreeData::backup(const ASTs & partitions, ContextPtr local_context)
{
    DataPartsVector data_parts;
    if (partitions.empty())
        data_parts = getDataPartsVector();
    else
        data_parts = getDataPartsVectorInPartitions(MergeTreeDataPartState::Committed, getPartitionIDsFromQuery(partitions, local_context));
    return backupDataParts(data_parts);
}
BackupEntries MergeTreeData::backupDataParts(const DataPartsVector & data_parts)