On Sat, Sep 20, 2014 at 3:38 AM, Greg Stark <stark@mit.edu> wrote:
>> > Is there a canonical case of where 'abort early' plans help? (I'm new
>> > to that term -- is it a recent planner innovation...got any handy
>> > links?)
>>
>> Yeah, here's an example of the canonical case:
>>
>> Table t1 ( a, b, c )
>>
>> - "b" is low-cardinality
>> - "c" is high-cardinality
>> - There are separate indexes on both b and c.
>>
>> SELECT a, b, c FROM t1
>> WHERE b = 2
>> ORDER BY c LIMIT 1;
>
> You badly want a partial index on c WHERE b=2 for each value of 2 which
> appears in your queries.
>
> It would be neat to have an opclass which worked like that. Which would
> amount to having prefix compression perhaps.
I've been looking at that exactly.
One complexity of it, is that splitting becomes much harder. As in, recursive.