| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
| Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Atri Sharma <atri(dot)jiit(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: A better way than tweaking NTUP_PER_BUCKET |
| Date: | 2014-01-27 18:00:54 |
| Message-ID: | CA+U5nMJsGwNV+Z8FMAcfNLJ30Ya-yKzhzZrVdjN+bY81gMX6dQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 27 January 2014 17:44, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> This topic is interesting - we found very bad performance with hashing large
> tables with high work_mem. MergeJoin with quicksort was significantly
> faster.
I've seen this also.
> I didn't deeper research - there is a possibility of virtualization
> overhead.
I took measurements and the effect was repeatable and happened for all
sizes of work_mem, but nothing more to add.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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