Re: [PATCH] Improve performance of NOTIFY over many databases (issue blocking on AccessExclusiveLock on object 0 of class 1262 of database 0)

On Tue, 23 Jul 2019 at 23:32, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Martijn van Oosterhout <kleptog(at)gmail(dot)com> writes:
> > I mean tracking the listening backends specifically, so you can
> > replace the loops:
> > for (i=0; i < MaxBackends; i++)
> > with
> > for (i=QUEUE_FIRST_LISTENING_BACKEND; i; i = QUEUE_NEXT_LISTENING_BACKEND(i))
>
> Ah ... but surely you would not put such info in AsyncQueueEntry,
> where there'd be a separate copy for each message. I think you
> meant to add the info to AsyncQueueControl.

Umm, yeah. Got that mixed up.

> It might be better to redefine the backends[] array as being mostly
> contiguous (ie, a new backend takes the first free slot not the one
> indexed by its own BackendId), at the price of needing to store
> BackendId in each slot explicitly instead of assuming it's equal to
> the array index. I suspect the existing data structure is putting too
> much of a premium on making sizeof(QueueBackendStatus) a power of 2.

This would require adding a "MyListenerId" to each backend which I'm not sure
helps the readability. And there's a chance of mixing the id up. The
power-of-2-ness
is I think indeed overrated.

I'll give it a shot a see how it looks.

Have a nice day,

--
Martijn van Oosterhout <kleptog(at)gmail(dot)com> http://svana.org/kleptog/