Re: WIP: extensible enums

On 10/19/2010 12:21 AM, Andrew Dunstan wrote:
>
>
> On 10/18/2010 10:52 AM, Tom Lane wrote:
>> We could possibly deal with enum types that follow the existing
>> convention if we made the cache entry hold a list of all the original,
>> known-to-be-sorted OIDs. (This could be reasonably compact and cheap to
>> probe if it were represented as a starting OID and a Bitmapset of delta
>> values, since we can assume that the initial set of OIDs is pretty close
>> together.) But we have to have that cache entry, and we have to consult
>> it on every single comparison, so it's definitely going to be slower
>> than before.
>>
>> So I'm thinking the comparison procedure goes like this:
>>
>> 1. Both OIDs even?
>> If so, just compare them numerically, and we're done.
>>
>> 2. Lookup cache entry for enum type.
>>
>> 3. Both OIDs in list of known-sorted OIDs?
>> If so, just compare them numerically, and we're done.
>>
>> 4. Search the part of the cache entry that lists sort positions.
>> If not both present, refresh the cache entry.
>> If still not present, throw error.
>>
>> 5. Compare by sort positions.
>>
>> Step 4 is the slowest part but would be avoided in most cases.
>> However, step 2 is none too speedy either, and would usually
>> be required when dealing with pre-existing enums.
>
> OK, I've made adjustments that I think do what you're suggesting.
>
>

I've discovered and fixed a couple more bugs in this. I have one or two
more things to fix and then I'll send a new patch.

Meanwhile, I've been testing a database that was upgraded from 9.0, so
it has a lot of odd-numbered Oids. It's not really clear from
performance testing that the bitmap is a huge win, or even a win at all.
(Of course, my implementation might suck too.) I'll continue testing.

cheers

andrew