Re: to-do item for explain analyze of hash aggregates?

On Mon, Apr 24, 2017 at 12:13 PM, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com
> wrote:

> On 04/24/2017 08:52 PM, Andres Freund wrote:
>
>> On 2017-04-24 11:42:12 -0700, Jeff Janes wrote:
>>
>>> The explain analyze of the hash step of a hash join reports something
>>> like
>>> this:
>>>
>>> -> Hash (cost=458287.68..458287.68 rows=24995368 width=37) (actual
>>> rows=24995353 loops=1)
>>> Buckets: 33554432 Batches: 1 Memory Usage: 2019630kB
>>>
>>>
>>> Should the HashAggregate node also report on Buckets and Memory Usage? I
>>> would have found that useful several times. Is there some reason this is
>>> not wanted, or not possible?
>>>
>>
>> I've wanted that too. It's not impossible at all.
>>
>>
> Why wouldn't that be possible? We probably can't use exactly the same
> approach as Hash, because hashjoins use custom hash table while hashagg
> uses dynahash IIRC. But why couldn't measure the amount of memory by
> looking at the memory context, for example?
>

He said "not impossible", meaning it is possible.

I've added it to the wiki Todo page. (Hopefully that has not doomed it to
be forgotten about)

Cheers,

Jeff