On Wed, Oct 6, 2010 at 6:31 PM, Ivan Voras <ivoras@xxxxxxxxxxx> wrote: > On 10/04/10 20:49, Josh Berkus wrote: > >>> The other major bottleneck they ran into was a kernel one: reading from >>> the heap file requires a couple lseek operations, and Linux acquires a >>> mutex on the inode to do that. The proper place to fix this is >>> certainly in the kernel but it may be possible to work around in >>> Postgres. >> >> Or we could complain to Kernel.org. They've been fairly responsive in >> the past. Too bad this didn't get posted earlier; I just got back from >> LinuxCon. >> >> So you know someone who can speak technically to this issue? I can put >> them in touch with the Linux geeks in charge of that part of the kernel >> code. > > Hmmm... lseek? As in "lseek() then read() or write()" idiom? It AFAIK > cannot be fixed since you're modifying the global "strean position" > variable and something has got to lock that. Well, there are lock free algorithms using CAS, no? > OTOH, pread() / pwrite() don't have to do that. Hey, I didn't know about those. That sounds like it might be worth investigating, though I confess I lack a 48-core machine on which to measure the alleged benefit. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
