**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 !currently_merging_mutating_parts.count(right);
        return !currently_merging_mutating_parts.count(left) && !currently_merging_mutating_parts.count(right)
            && getCurrentMutationVersion(left, lock) == getCurrentMutationVersion(right, lock) && partsContainSameProjections(left, right);
    };
    SelectPartsDecision select_decision = SelectPartsDecision::CANNOT_SELECT;
    if (partition_id.empty())
    {
        UInt64 max_source_parts_size = merger_mutator.getMaxSourcePartsSizeForMerge();
        bool merge_with_ttl_allowed = getTotalMergesWithTTLInMergeList() < data_settings->max_number_of_merges_with_ttl_in_pool;
        
        
        
        if (max_source_parts_size > 0)
        {
            select_decision = merger_mutator.selectPartsToMerge(
                future_part,
                aggressive,
                max_source_parts_size,
                can_merge,
                merge_with_ttl_allowed,
                out_disable_reason);
        }
        else if (out_disable_reason)
            *out_disable_reason = "Current value of max_source_parts_size is zero";
    }
    else
    {
        while (true)
        {
            UInt64 disk_space = getStoragePolicy()->getMaxUnreservedFreeSpace();