On Sat, Sep 24, 2011 at 4:16 PM, Magnus Hagander <mag...@hagander.net> wrote: > I was assuming the kernel was smart enough to read this as "*this* > process is not going to be using this file anymore", not "nobody in > the whole machine is going to use this file anymore". And the process > running the base backup is certainly not going to read it again. > > But that's a good point - do you know if that is the case, or does it > mandate more testing?
It's not the case on Linux. I used to use DONTNEED to flush pages from cache before running a benchmark. I verified with mincore that the pages were actually getting removed from cache. Sometimes there was the occasional straggler but nearly all got flushed and after a second or third pass the stragglers were gone too. In case you're wondering, this was because using /proc/.../drop_caches caused flaky benchmarks. My theory was that it was causing pages of the executable to trigger page faults in the middle of the benchmark. -- greg -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers