Re: Parallel Aggregates for string_agg and array_agg

On 03/28/2018 03:54 PM, Tom Lane wrote:
> Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
>> On 03/28/2018 05:28 AM, Tom Lane wrote:
>>> Getting a solution that would work for other polymorphic serialization
>>> functions seems like a bit of a research project to me. In the meantime,
>>> I think David's right that what we need to look at is the actual input
>>> type of the aggregate, and then assume that what's to be serialized is
>>> an array of that. Conceivably an aggregate could be built that uses
>>> these serial/deserial functions and yet its input type is something else
>>> than what it constructs an array of ... but I find it a bit hard to
>>> wrap my brain around what that would be exactly.
>
>> But David's fix doesn't check the aggregate to produce an array of the
>> input type (or anyarray). It could easily be an aggregate computing a
>> bloom filter or something like that, which has no such issues in the
>> serial/deserial functions.
>
> Oh, if he's not restricting it to these serialization functions, I
> agree that seems wrong. I thought the discussion was about what to
> do after checking the functions.
>

Nope, David's patch does not check what the serial/deserial functions
are (and checks aggref->aggargtypes directly, not the exprType thing).

>> Also, if it's checking aggref->aggargtypes, it'll reject anyelement
>> parameters, no?
>
> I had in mind to look at exprType() of the argument.
>

Right, I'm fine with that.

regards

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