Re: change in LOCK behavior

Simon Riggs <simon@2ndQuadrant.com> writes:
> On 11 October 2012 01:43, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I think we have to revert and go back to the drawing board on this.

> Given that change was also sold on the basis of higher performance, I
> suggest we retest performance to check there is a gain. If there is
> still a gain, I suggest we add this as a SIGHUP option, default to
> off, rather than completely remove it.

I'm not in favor of adding a GUC for this.  The right fix is to redesign
the locking/snapshotting process, not expose its warts in bizarre little
knobs that make users deal with the tradeoffs.

Maybe what we really need is to find a way to make taking a snapshot a
lot cheaper, such that the whole need for this patch goes away.  We're
not going to get far with the idea of making SnapshotNow MVCC-safe
unless it becomes a lot cheaper to get an MVCC snapshot.  I recall some
discussion of trying to reduce a snapshot to a WAL offset --- did that
idea crash and burn, or is it still viable?

Anyway, I believe that for now we ought to revert and rethink, not look
for band-aid ways of preserving this patch.
        regards, tom lane