Re: Default setting for enable_hashagg_disk
От | Tomas Vondra |
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Тема | Re: Default setting for enable_hashagg_disk |
Дата | |
Msg-id | 20200626144414.rftlidu34rigiulv@development обсуждение исходный текст |
Ответ на | Re: Default setting for enable_hashagg_disk (Bruce Momjian <bruce@momjian.us>) |
Ответы |
Re: Default setting for enable_hashagg_disk
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Список | pgsql-hackers |
On Fri, Jun 26, 2020 at 12:02:10AM -0400, Bruce Momjian wrote: >On Fri, Jun 26, 2020 at 01:53:57AM +0200, Tomas Vondra wrote: >> I'm not saying it's not beneficial to use different limits for different >> nodes. Some nodes are less sensitive to the size (e.g. sorting often >> gets faster with smaller work_mem). But I think we should instead have a >> per-session limit, and the planner should "distribute" the memory to >> different nodes. It's a hard problem, of course. > >Yeah, I am actually confused why we haven't developed a global memory >allocation strategy and continue to use per-session work_mem. > I think it's pretty hard problem, actually. One of the reasons is that the costing of a node depends on the amount of memory available to the node, but as we're building the plan bottom-up, we have no information about the nodes above us. So we don't know if there are operations that will need memory, how sensitive they are, etc. And so far the per-node limit served us pretty well, I think. So I'm not very confused we don't have the per-session limit yet, TBH. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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