>
> On Mon, 16 Mar 1998, David Gould wrote:
>
> > The generic way to do this is
> >
> > select( NULL_FDSET, NULL_FDSET, NULL_FDSET, &delaytime, NULL);
> >
> > Delay time may be 0, but a random value between 0 and say 30 msec seems
> > to be optimal. Hard busy wait spinlocks cause huge performance problems with
> > heavily loaded systems and lots of postgres backends. Basically one backend
> > ends up with the lock and gets scheduled out holding it, every else queues
> > up busywaiting behind this one. But the backend holding the lock cannot
> > release it until all the other backeds waiting on the lock exhaust a full
> > timeslice busywaiting. Get 20 of these guys going (like on a busy website) and
> > the system pretty much stops doing any work at all.
> >
> > I say we should get this in as soon as we can.
>
> Can you submit an appropriate patch that can be included in the mega-patch
> to be created on Sunday?
Just a warning that this is not going to be easy. We have OS-specific
code for spinlocks in include/storage/s_lock.h and
backend/storage/buffer/s_lock.c. So each S_LOCK macro call has to have
its test-and-set logic de-coupled with its while-lock-fail-try-again
logic. Most of them are easy, but some like VAX:
#define S_LOCK(addr) __asm__("1: bbssi $0,(%0),1b": :"r"(addr))
are hard to de-couple. Now, I did not know we supported NetBSD on VAX.
Does it work, anyone? Can I remove it?
This is going to be pretty tough to test on every platform we support,
so if it is done now, it will have to be done carefully.
--
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