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    SubjectRe: kernel lock contention and scalability
    On Tue, 6 Mar 2001, Jonathan Lahr wrote:

    [ sorry to reply over another reply, but I don't have
    the original of this ]

    > > Tridge and I tried out the postgresql benchmark you used here and this
    > > contention is due to a bug in postgres. From a quick strace, we found
    > > the threads do a load of select(0, NULL, NULL, NULL, {0,0}).

    I can shed some light on this (though I'm far from a PG hacker).

    Postgres can use either of two locking methods -- SysV semaphores
    (which it tries to avoid, asusming that they'll be too heavy) or
    userspace spinlocks (via inline assembler on platforms which support

    In the slow path of a spinlock_acquire they busy wait for a few
    cycles, and then call schedule with a zero timeout assuming that
    it'll basically do the same as a sched_yield() but more portably.


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