**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.
virtual void checkAlterIsPossible(const AlterCommands & commands, ContextPtr context) const;
    /**
      * Checks that mutation commands can be applied to storage.
      */
    virtual void checkMutationIsPossible(const MutationCommands & commands, const Settings & settings) const;
    /** ALTER tables with regard to its partitions.
      * Should handle locks for each command on its own.
      */
    virtual Pipe alterPartition(
        const StorageMetadataPtr & ,
        const PartitionCommands & ,
        ContextPtr );
    
    virtual void checkAlterPartitionIsPossible(const PartitionCommands & commands, const StorageMetadataPtr & metadata_snapshot, const Settings & settings) const;
    /** Perform any background work. For example, combining parts in a MergeTree type table.
      * Returns whether any work has been done.
      */
    virtual bool optimize(
        const ASTPtr & ,
        const StorageMetadataPtr & ,
        const ASTPtr & ,
        bool ,
        bool ,
        const Names & ,
        ContextPtr )
    {
        throw Exception("Method optimize is not supported by storage " + getName(), ErrorCodes::NOT_IMPLEMENTED);
    }
    
    virtual void mutate(const MutationCommands &, ContextPtr)