Re: [HACKERS] Poor memory context performance in large hash joins

On 02/27/2017 12:55 PM, Andres Freund wrote:
> On 2017-02-24 15:18:04 -0800, Andres Freund wrote:
>> On 2017-02-24 15:12:37 -0800, Andres Freund wrote:
>>> On 2017-02-24 18:04:18 -0500, Tom Lane wrote:
>>>> Concretely, something like the attached.  This passes regression tests
>>>> but I've not pushed on it any harder than that.
>>>
>>> Heh, I'd just gotten something that didn't immediately crash anymore ;)
>>>
>>> Running your patch against Jeff's test-case, verified before that I
>>> could easily reproduce the O(N^2) cost.
>>
>> Oh, that didn't take as long as I was afraid (optimized/non-assert build):
>>
>> postgres[26268][1]=# SET work_mem = '13GB';
>> SET
>> Time: 2.591 ms
>> postgres[26268][1]=# select count(*) from foobar2 where not exists (select 1 from foobar t where
t.titleid=foobar2.titleid);
>> Time: 268043.710 ms (04:28.044)
>
> As another datapoint, I measured this patch against the problem from
> https://www.postgresql.org/message-id/20170227111732.vrx5v72ighehwpkf@alap3.anarazel.de
> (see top post in thread), and it indeed fixes the runtime issue -
> there's still considerably higher memory usage and some runtime
> overhead, but the quadratic behaviour is gone.
>
> I think we should go forward with something like this patch in all
> branches, and only use Tomas' patch in master, because they're
> considerably larger.
>

So you've tried to switch hashjoin to the slab allocators? Or what have 
you compared?

regards

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