Re: Trouble with hashagg spill I/O pattern and costing
От | Tomas Vondra |
---|---|
Тема | Re: Trouble with hashagg spill I/O pattern and costing |
Дата | |
Msg-id | 20200521191739.hi7g7rhhv6txxrwc@development обсуждение исходный текст |
Ответ на | Re: Trouble with hashagg spill I/O pattern and costing (Jeff Davis <pgsql@j-davis.com>) |
Список | pgsql-hackers |
On Thu, May 21, 2020 at 12:04:19PM -0700, Jeff Davis wrote: >On Thu, 2020-05-21 at 20:54 +0200, Tomas Vondra wrote: >> The last column is master with the tlist tweak alone - it's better >> than >> hashagg on master alone, but it's not nearly as good as with both >> tlist >> and prealloc patches. > >Right, I certainly think we should do the prealloc change, as well. > >I'm tweaking the patch to be a bit more flexible. I'm thinking we >should start the preallocation list size ~8 and then double it up to >~128 (depending on your results). That would reduce the waste in case >we have a large number of small partitions. > You're reading my mind ;-) I don't think 128 is necessarily the maximum we should use - it's just that I haven't tested higher values. I wouldn't be surprised if higher values made it a bit faster. But we can test and tune that, I agree with growing the number of pre-allocted blocks over time. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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