Re: lazy vxid locks, v2

On Tue, 2011-07-05 at 13:15 -0400, Robert Haas wrote:
> On Tue, Jul 5, 2011 at 1:13 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > Here is an updated version of the "lazy vxid locks" patch [1], which
> > applies over the latest "reduce the overhead of frequent table
> > locks"[2] patch.
> >
> > [1] https://commitfest.postgresql.org/action/patch_view?id=585
> > [2] https://commitfest.postgresql.org/action/patch_view?id=572
>
> And then I forgot the attachment.

The patch looks good, and I like the concept.

My only real comment is one that you already made: the
BackendIdGetProc() mechanism is not "awesome". However, that seems like
material for a separate patch, if at all.

Big disclaimer: I did not do any performance review, despite the fact
that this is a performance patch.

I see that there are some active performance concerns around this patch,
specifically that it may cause an increase in spinlock contention:

http://archives.postgresql.org/message-id/BANLkTikp4EGbfw9xDx9bQ_vK8DQa11WbPg@mail.gmail.com

Fortunately, there's a subsequent discussion that shows a lot of
promise:

http://archives.postgresql.org/pgsql-hackers/2011-07/msg00293.php

I'll mark this "waiting on author" pending the results of that
discussion.

I like the approach you're taking with this series of patches, so
perhaps we shouldn't set the bar so high that you have to remove all of
the bottlenecks before making any progress. Then again, maybe there's
not a huge cost to leaving these patches on the shelf until we're sure
that they lead somewhere.

Regards,
Jeff Davis