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

Heikki Linnakangas  writes:
> On 21.02.2012 13:19, Fujii Masao wrote:
>> In some places, the spinlock "insertpos_lck" is taken while another
>> spinlock "info_lck" is being held. Is this OK? What if unfortunately
>> inner spinlock takes long to be taken?

> Hmm, that's only done at a checkpoint (and a restartpoint), so I doubt 
> that's a big issue in practice. We had the same pattern before the 
> patch, just with WALInsertLock instead of insertpos_lck. Holding a 
> spinlock longer is much worse than holding a lwlock longer, but 
> nevertheless I don't think that's a problem.

No, that's NOT okay.  A spinlock is only supposed to be held across a
short straight-line sequence of instructions.  Something that could
involve a spin loop, or worse a sleep() kernel call, is right out.
Please change this.
		regards, tom lane