Horton

Re: foreign key locks, 2nd attempt

Alvaro Herrera <alvherre@commandprompt.com>

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From: Alvaro Herrera <alvherre@commandprompt.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Simon Riggs <simon@2ndquadrant.com>, Noah Misch <noah@leadboat.com>, Tom Lane <tgl@sss.pgh.pa.us>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2012-03-16T00:53:05Z
Lists: pgsql-hackers

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  1. Try to avoid running with a full fsync request queue.

Excerpts from Robert Haas's message of jue mar 15 21:37:36 -0300 2012:
> 
> On Thu, Mar 15, 2012 at 5:07 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> > On Wed, Mar 14, 2012 at 5:23 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> >>> You still have HEAP_XMAX_{INVALID,COMMITTED} to reduce the pressure on mxid
> >>> lookups, so I think something more sophisticated is needed to exercise that
> >>> cost.  Not sure what.
> >>
> >> I don't think HEAP_XMAX_COMMITTED is much help, because committed !=
> >> all-visible.
> >
> > So because committed does not equal all visible there will be
> > additional lookups on mxids? That's complete rubbish.
> 
> Noah seemed to be implying that once the updating transaction
> committed, HEAP_XMAX_COMMITTED would get set and save the mxid lookup.
>  But I think that's not true, because anyone who looks at the tuple
> afterward will still need to know the exact xmax, to test it against
> their snapshot.

Yeah, we don't set HEAP_XMAX_COMMITTED on multis, even when there's an
update in it and it committed.  I think we could handle it, at least
some of the cases, but that'd require careful re-examination of all the
tqual.c code, which is not something I want to do right now.

-- 
Álvaro Herrera <alvherre@commandprompt.com>
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