Re: Spilling hashed SetOps and aggregates to disk

On 06/06/2018 04:01 PM, Andres Freund wrote:
> Hi,
> 
> On 2018-06-06 15:58:16 +0200, Tomas Vondra wrote:
>> The other issue is that serialize/deserialize is only a part of a problem -
>> you also need to know how to do "combine", and not all aggregates can do
>> that ... (certainly not in universal way).
> 
> There are several schemes where only serialize/deserialize are needed,
> no?  There are a number of fairly sensible schemes where there won't be
> multiple transition values for the same group, no?
> 

Possibly, not sure what schemes you have in mind exactly ...

But if you know there's only a single transition value, why would you 
need serialize/deserialize at all. Why couldn't you just finalize the 
value and serialize that?

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
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