[DISCUSS] Is dictionary bit width == 0 allowed?

[Antoine Pitrou]

Hello,

Using dictionary encoding, it is very easy to create a compression bomb 
simply by setting bit width = 0. Then you can encode a virtually 
infinite number of values in a constant (very small) data size. This is 
an ideal payload for a potential denial of service, either through CPU 
or memory exhaustion.

Looking at the dictionary encoder in Arrow C++, bit width == 0 is only 
emitted when there are 0 physical values to encode. Do other encoders 
have different policies? Would it be reasonable to state that bit width 
== 0 is only allowed if there are zero physical values in the page?

Regards

Antoine.