On Wed, Jan 15, 2014 at 06:14:18PM -0600, Jim Nasby wrote: > On 1/15/14, 12:00 AM, Claudio Freire wrote: > >My completely unproven theory is that swapping is overwhelmed by > >near-misses. Ie: a process touches a page, and before it's > >actually swapped in, another process touches it too, blocking on > >the other process' read. But the second process doesn't account > >for that page when evaluating predictive models (ie: read-ahead), > >so the next I/O by process 2 is unexpected to the kernel. Then > >the same with 1. Etc... In essence, swap, by a fluke of its > >implementation, fails utterly to predict the I/O pattern, and > >results in far sub-optimal reads. > > > >Explicit I/O is free from that effect, all read calls are > >accountable, and that makes a difference. > > > >Maybe, if the kernel could be fixed in that respect, you could > >consider mmap'd files as a suitable form of temporary storage. > >But that would depend on the success and availability of such a > >fix/patch. > > Another option is to consider some of the more "radical" ideas in > this thread, but only for temporary data. Our write sequencing and > other needs are far less stringent for this stuff. -- Jim C.
I suspect that a lot of the temporary data issues can be solved by using tmpfs for temporary files.... Cheers, Dave. -- Dave Chinner da...@fromorbit.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers