**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.
else
    {
        {
            changeSettings(new_metadata.settings_changes, table_lock_holder);
            checkTTLExpressions(new_metadata, old_metadata);
            
            setProperties(new_metadata, old_metadata);
            DatabaseCatalog::instance().getDatabase(table_id.database_name)->alterTable(local_context, table_id, new_metadata);
            if (!maybe_mutation_commands.empty())
                mutation_version = startMutation(maybe_mutation_commands, mutation_file_name);
        }
        
        
        if (!maybe_mutation_commands.empty())
            waitForMutation(mutation_version, mutation_file_name);
    }
    {
        
        auto new_storage_settings = getSettings();
        if (old_storage_settings->non_replicated_deduplication_window != new_storage_settings->non_replicated_deduplication_window)
        {
            
            
            if (new_storage_settings->non_replicated_deduplication_window != 0 && format_version < MERGE_TREE_DATA_MIN_FORMAT_VERSION_WITH_CUSTOM_PARTITIONING)
                throw Exception("Deduplication for non-replicated MergeTree in old syntax is not supported", ErrorCodes::BAD_ARGUMENTS);
            deduplication_log->setDeduplicationWindowSize(new_storage_settings->non_replicated_deduplication_window);
        }
    }
}
CurrentlyMergingPartsTagger::CurrentlyMergingPartsTagger(