Re: slow startup due to LWLockAssign() spinlock

On 2014-04-24 23:28:14 +0200, Andres Freund wrote:
> On 2014-04-24 12:43:13 -0400, Tom Lane wrote:
> > Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > > On 2014-04-24 11:02:44 -0400, Tom Lane wrote:
> > >> FWIW, I like the LWLockAssignBatch idea a lot better than the currently
> > >> proposed patch. LWLockAssign is a low-level function that has no business
> > >> making risky assumptions about the context it's invoked in.
> >
> > > I don't think LWLockAssignBatch() is that easy without introducing
> > > layering violations. It can't just return a pointer out of the main
> > > lwlock array that then can be ++ed clientside because MainLWLockArray's
> > > stride isn't sizeof(LWLock).
> >
> > Meh. I knew this business of using pointers instead of indexes would
> > have some downsides.
> >
> > We could return the array stride ... kinda ugly, but since there's
> > probably only one consumer for this API, it's not *that* bad. Could
> > wrap the stride-increment in a macro, perhaps.
>
> I think I am just going to wait for 9.5 where I sure hope we can
> allocate the buffer lwlocks outside the main array...

For reference (and backup), here's my current patch for that.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services