Re: WIP: extensible enums

Andrew Dunstan <andrew@dunslane.net> writes:
> On 10/17/2010 01:20 PM, Tom Lane wrote:
>> The way I'd be inclined to design this is that altering an enum doesn't
>> change its pg_type entry at all, just add another row to pg_enum.
>> When first needing to compare values of an enum, load up the typcache
>> entry for it.

> Perhaps mistakenly I wanted to avoid doing that as it would slow down a 
> retail comparison quite a lot, especially in the case of an enum with a 
> very large label set. That's why I put the sorted property and label 
> count in pg_type.

Just going back to this point: I don't buy that argument at all.
If you have to consult pg_type to find out whether fast or slow
comparison is needed, you've already burned all the cycles required
for a cache lookup.  The only way that a large typcache entry would
really be a performance issue compared to just consulting pg_type
is if it had to be refreshed a lot, which doesn't seem like a likely
problem.
        regards, tom lane