**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.
reserved_space
                = storage.tryReserveSpacePreferringTTLRules(metadata_snapshot, total_size, ttl_infos, time(nullptr), max_volume_index);
    }
    if (!reserved_space)
    {
        if (is_mutation)
            throw Exception("Not enough space for mutating part '" + future_part->parts[0]->name + "'", ErrorCodes::NOT_ENOUGH_SPACE);
        else
            throw Exception("Not enough space for merging parts", ErrorCodes::NOT_ENOUGH_SPACE);
    }
    future_part->updatePath(storage, reserved_space.get());
    for (const auto & part : future_part->parts)
    {
        if (storage.currently_merging_mutating_parts.count(part))
            throw Exception("Tagging already tagged part " + part->name + ". This is a bug.", ErrorCodes::LOGICAL_ERROR);
    }
    storage.currently_merging_mutating_parts.insert(future_part->parts.begin(), future_part->parts.end());
}
CurrentlyMergingPartsTagger::~CurrentlyMergingPartsTagger()
{
    std::lock_guard lock(storage.currently_processing_in_background_mutex);
    for (const auto & part : future_part->parts)
    {
        if (!storage.currently_merging_mutating_parts.count(part))
            std::terminate();
        storage.currently_merging_mutating_parts.erase(part);
    }
    storage.currently_processing_in_background_condition.notify_all();
}
Int64 StorageMergeTree::startMutation(const MutationCommands & commands, String & mutation_file_name)