Thread: Add os_page_num to pg_buffercache
Hi hackers, I was doing some more tests around ba2a3c2302f (pg_buffercache_numa) and thought that seeing how buffers are spread across multiple OS pages (if that's the case) thanks to the os_page_num field is good information to have. The thing that I think is annoying is that to get this information (os_page_num): - One needs to use pg_buffercache_numa (which is more costly/slower) than pg_buffercache - One needs a system with NUMA support enabled So why not also add this information (os_page_num) in pg_buffercache? - It would make this information available on all systems, not just NUMA-enabled ones - It would help understand the memory layout implications of configuration changes such as database block size, OS page size (huge pages for example) and see how the buffers are spread across OS pages (if that's the case). So, please find attached a patch to $SUBJECT then. Remarks: - Maybe we could create a helper function to reduce the code duplication between pg_buffercache_pages() and pg_buffercache_numa_pages() - I think it would have made sense to also add this information while working on ba2a3c2302f but (unfortunately) I doubt that this patch is candidate for v18 post freeze (it looks more a feature enhancement than anything else) - It's currently doing the changes in pg_buffercache v1.6 but will need to create v1.7 for 19 (if the above stands true) Looking forward to your feedback, Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
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On 4/10/25 15:17, Bertrand Drouvot wrote: > Hi hackers, > > I was doing some more tests around ba2a3c2302f (pg_buffercache_numa) and > thought that seeing how buffers are spread across multiple OS pages (if that's > the case) thanks to the os_page_num field is good information to have. > > The thing that I think is annoying is that to get this information (os_page_num): > > - One needs to use pg_buffercache_numa (which is more costly/slower) than pg_buffercache > - One needs a system with NUMA support enabled > > So why not also add this information (os_page_num) in pg_buffercache? > > - It would make this information available on all systems, not just NUMA-enabled ones > - It would help understand the memory layout implications of configuration changes > such as database block size, OS page size (huge pages for example) and see how the > buffers are spread across OS pages (if that's the case). > > So, please find attached a patch to $SUBJECT then. > > Remarks: > > - Maybe we could create a helper function to reduce the code duplication between > pg_buffercache_pages() and pg_buffercache_numa_pages() > - I think it would have made sense to also add this information while working > on ba2a3c2302f but (unfortunately) I doubt that this patch is candidate for v18 > post freeze (it looks more a feature enhancement than anything else) > - It's currently doing the changes in pg_buffercache v1.6 but will need to > create v1.7 for 19 (if the above stands true) > This seems like a good idea in principle, but at this point it has to wait for PG19. Please add it to the July commitfest. regards -- Tomas Vondra
On Thu, Apr 10, 2025 at 03:35:24PM +0200, Tomas Vondra wrote: > This seems like a good idea in principle, but at this point it has to > wait for PG19. Please add it to the July commitfest. +1. From a glance, this seems to fall in the "new feature" bucket and should likely wait for v19. -- nathan
Hi, On Thu, Apr 10, 2025 at 09:58:18AM -0500, Nathan Bossart wrote: > On Thu, Apr 10, 2025 at 03:35:24PM +0200, Tomas Vondra wrote: > > This seems like a good idea in principle, but at this point it has to > > wait for PG19. Please add it to the July commitfest. > > +1. From a glance, this seems to fall in the "new feature" bucket and > should likely wait for v19. Thank you both for providing your thoughts that confirm my initial doubt. Let's come back to that one later then. Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com