Can I disable the completion of ":!" in cmdline?

[Dice21]

It takes too much time to complete the "!" command on my device.
So is there any way to disable it?

[Shougo]

Please see this.

#821

[Dice21]

Thank you too much. Before I searched for "!" in Issues and got nothing.
Now i set completion.keyword_length to 3 and it works for me.