| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Noah Misch <noah(at)leadboat(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: foreign key locks, 2nd attempt |
| Date: | 2012-03-16 00:37:36 |
| Message-ID: | CA+TgmoZx300pkRkL27-ejWAcHCp-6-1MuyMvotJZqX91qyzOtA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Mar 15, 2012 at 5:07 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Wed, Mar 14, 2012 at 5:23 PM, Robert Haas <robertmhaas(at)gmail(dot)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.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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