Re: Re: custom hash-based COUNT(DISTINCT) aggregate - unexpectedly high memory consumption

From: Tomas Vondra <tv(at)fuzzy(dot)cz>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: custom hash-based COUNT(DISTINCT) aggregate - unexpectedly high memory consumption
Date: 2013-10-07 21:02:20
Message-ID: 5253215C.1050500@fuzzy.cz
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Hi Atri!

On 7.10.2013 16:56, Atri Sharma wrote:
>>> 3. Consider dropping buckets in favor of open addressing (linear
>>> probing, quadratic, whatever). This avoids another level of
>>> pointer indirection.
>>
>> OK, this sounds really interesting. It should be fairly
>> straightforward for fixed-length data types (in that case I can get
>> rid of the pointers altogether).
>>
> Consider the aspects associated with open addressing.Open addressing
> can quickly lead to growth in the main table.Also, chaining is a much
> cleaner way of collision resolution,IMHO.

What do you mean by "growth in the main table"?

Tomas

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