**Describe the bug**

I have a table like:

```
CREATE TABLE test (
    time DateTime64(3)
    ...
) ENGINE = MergeTree()
PARTITION BY toStartOfInterval(time, INTERVAL 1 HOUR)
...
```

But when I search in `system.parts` it does not appear to have the `min/max` columns appropriately set?

```
partition:                             2020-06-01 01:00:00
min_date:                              1970-01-01
max_date:                              1970-01-01
min_time:                              1970-01-01 00:00:00
max_time:                              1970-01-01 00:00:00
```

I assume that if these were correctly set, doing a `select toStartOfInterval(time, interval 1 day), count()` type query would be pretty instant rather than trying to scan everything? I am guessing this is due to the `DateTime64` type in use?

Clickhouse 20.11.3.3

{
                String file_name = fileName(relative_path);
                if (file_name.empty())
                    throw Exception("relative_path " + relative_path + " of part " + name + " is invalid or not set", ErrorCodes::LOGICAL_ERROR);
                if (!startsWith(file_name, "tmp"))
                {
                    LOG_ERROR(storage.log, "~DataPart() should remove part {} but its name doesn't start with tmp. Too suspicious, keeping the part.", path);
                    return;
                }
            }
            remove(false);
            if (state == State::DeleteOnDestroy)
            {
                LOG_TRACE(storage.log, "Removed part from old location {}", path);
            }
        }
        catch (...)
        {
            tryLogCurrentException(__PRETTY_FUNCTION__);
        }
    }
}
UInt64 IMergeTreeDataPart::getIndexSizeInBytes() const
{
    UInt64 res = 0;
    for (const ColumnPtr & column : index)
        res += column->byteSize();
    return res;
}
UInt64 IMergeTreeDataPart::getIndexSizeInAllocatedBytes() const