From: | Mischa Sandberg <mischa(dot)sandberg(at)sophos(dot)com> |
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To: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Postgresql on multi-core CPU's: is this old news? |
Date: | 2011-04-05 18:21:58 |
Message-ID: | CB0F73E165CFFA4496D12161D835562C030AE939BA@US-COL-EXCHMBX1.green.sophos |
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Lists: | pgsql-hackers |
Came across the following in a paper from Oct 2010. Was wondering is this is old news I missed in this group.
http://pdos.csail.mit.edu/papers/linux:osdi10.pdf
about Linux optimization on multi-core CPU's.
The group at MIT were exploring how some Linux apps were scaling up --- sometimes badly, mostly due to hidden contention over cache-line consistency across the cores' caches.
In a nutshell: if an app, or the system calls it uses, tries to modify anything in a cache line (32-64 byte slice of memory) that another core is using, there's a lot of fumbling in the dark to make sure there is no conflict. When I saw PostgreSQL named in the abstract, I thought, "Aha! Contention over shm". Not so. Skip to page 11 (section 5.5) for most of the PG specifics.
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