Re: [RFC] new digest datatypes, or generic fixed-len hex types?

On Jul 28, 2009, at 6:15 AM, Peter Eisentraut wrote:
> On Monday 27 July 2009 14:50:30 Alvaro Herrera wrote:
>> We've developed some code to implement fixed-length datatypes for  
>> well
>> known digest function output (MD5, SHA1 and the various SHA2 types).
>> These types have minimal overhead and are quite complete, including
>> btree and hash opclasses.
>>
>> We're wondering about proposing them for inclusion in pgcrypto.  I  
>> asked
>> Marko Kreen but he is not sure about it; according to him it would be
>> better to have general fixed-length hex types.  (I guess it would be
>> possible to implement the digest types as domains over those.)
>
> I think equipping bytea with a length restriction would be a very  
> natural,
> simple, and useful addition.  If we ever want to move the bytea  
> type closer to
> the SQL standard blob type, this will need to happen anyway.
>
> The case for separate fixed-length data types seems very dubious,  
> unless you
> can show very impressive performance numbers.  For one thing, they  
> would make
> the whole type system more complicated, or in the alternative,  
> would have
> little function and operator support.
bytea doesn't cast well to and from text when you're dealing with hex  
data; you end up using the same amount of space as a varchar. What  
would probably work well is a hex datatype that internally works like  
bytea but requires that the input data is hex (I know you can use  
encode/decode, but that added step is a pain). A similar argument  
could be made for base64 encoded data.
-- 
Decibel!, aka Jim C. Nasby, Database Architect  decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828