Re: Scaling XLog insertion (was Re: Moving more work outside WALInsertLock)

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> On 06.03.2012 14:52, Fujii Masao wrote:
>> This also strikes me that the usage of the spinlock insertpos_lck might
>> not be OK in ReserveXLogInsertLocation() because a few dozen instructions
>> can be performed while holding the spinlock....

> I admit that block is longer than any of our existing spinlock blocks. 
> However, it's important for performance. I tried using a lwlock earlier, 
> and that negated the gains. So if that's a serious objection, then let's 
> resolve that now before I spend any more time on other aspects of the 
> patch. Any ideas how to make that block shorter?

How long is the current locked code exactly --- does it contain a loop?

I'm not sure where the threshold of pain is for length of time holding a
spinlock.  I wouldn't go out of the way to avoid using a spinlock for
say a hundred instructions, at least not unless it was a very
high-contention lock.  But sleeping while holding a spinlock is right out.
        regards, tom lane