Re: checkpointer continuous flushing
От | Fabien COELHO |
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Тема | Re: checkpointer continuous flushing |
Дата | |
Msg-id | alpine.DEB.2.10.1508180828270.11520@sto обсуждение исходный текст |
Ответ на | Re: checkpointer continuous flushing (Amit Kapila <amit.kapila16@gmail.com>) |
Ответы |
Re: checkpointer continuous flushing
Re: checkpointer continuous flushing |
Список | pgsql-hackers |
Hello Amit, >> So the option is best kept as "off" for now, without further data, I'm >> fine with that. > > One point to think here is on what basis user can decide make > this option on, is it predictable in any way? > I think one case could be when the data set fits in shared_buffers. Yep. > In general, providing an option is a good idea if user can decide with > ease when to use that option or we can give some clear recommendation > for the same otherwise one has to recommend that test your workload with > this option and if it works then great else don't use it which might > also be okay in some cases, but it is better to be clear. My opinion, which is not backed by any data (anyone can feel free to provide a FreeBSD box for testing...) is that it would mostly be an improvement if you have a significant write load to have the flush option on when running on non-Linux systems which provide posix_fadvise. If you have a lot of reads and few writes, then postgresql currently works reasonably enough, which is why people do not complain too much about write stalls, and I expect that the situation would not be significantly degraded. Now there are competing positive and negative effects induced by using posix_fadvise, and moreover its implementation varries from OS to OS, so without running some experiments it is hard to be definite. > One minor point, while glancing through the patch, I noticed that couple > of multiline comments are not written in the way which is usually used > in code (Keep the first line as empty). Indeed. Please find attached a v10, where I have reviewed comments for style & contents, and also slightly extended the documentation about the flush option to hint that it is essentially useful for high write loads. Without further data, I think it is not obvious to give more definite advices. -- Fabien.
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