Re: slow startup due to LWLockAssign() spinlock

On 2014-02-03 11:22:45 -0500, Tom Lane wrote:
> Andres Freund <andres@2ndquadrant.com> writes:
> > On larger, multi-socket, machines, startup takes a fair bit of time. As
> > I was profiling anyway I looked into it and noticed that just about all
> > of it is spent in LWLockAssign() called by InitBufferPool(). Starting
> > with shared_buffers=48GB on the server Nate Boley provided, takes about
> > 12 seconds. Nearly all of it spent taking the ShmemLock spinlock.
> > Simply modifying LWLockAssign() to not take the spinlock when
> > !IsUnderPostmaster speeds it up to 2 seconds. While certainly not making
> > LWLockAssign() prettier it seems enough of a speedup to be worthwile
> > nonetheless.
>
> Hm.  This patch only works if the postmaster itself never assigns any
> LWLocks except during startup.  That's *probably* all right, but it
> seems a bit scary.  Is there any cheap way to make the logic actually
> be what your comment claims, namely "Interlocking is not necessary during
> postmaster startup"?  I guess we could invent a ShmemInitInProgress global
> flag ...

So, here's a flag implementing things with that flag. I kept your name,
as it's more in line with ipci.c's naming, but it looks kinda odd
besides proc_exit_inprogress.

Greetings,

Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
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