On Wed, Jan 5, 2011 at 3:06 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Jan 5, 2011 at 3:00 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> On Mon, 2011-01-03 at 23:13 -0500, Robert Haas wrote:
>>> > Hmmm, my earlier code took xmax only if xmax > xmin. That was wrong;
>>> > what I have now is better, but your point is there may be an even better
>>> > truth. I'll think on that a little more.
>> I remember that I thought some more on this and decided that I couldn't
>> see a problem. I also see I didn't update the list to say that.
>>> I guess the problem case here is something like:
>>> 1. T1 begins. T1 writes a tuple A (so it gets an XID).
>>> 2. T2 begins. T2 writes a tuple B (so it gets a later XID).
>>> 3. T1 takes a new snapshot that can see B and deletes B.
>>> 4. T2 commits.
>>> 5. T1 commits.
>> How is step (3) possible before step (4)?
> At read committed isolation level, which is the default, we take a new
> snapshot after every command.
Oh, I'm a dork. You're saying T2 hasn't committed yet. Let me think
about this some more...
The Enterprise PostgreSQL Company
In response to
pgsql-hackers by date
|Next:||From: Jesper Krogh||Date: 2011-01-05 20:22:54|
|Subject: Re: crash-safe visibility map, take three|
|Previous:||From: Jeff Davis||Date: 2011-01-05 20:07:32|
|Subject: Re: WIP: Range Types|
pgsql-committers by date
|Next:||From: Bruce Momjian||Date: 2011-01-06 01:15:32|
|Subject: pgsql: Rename pg_upgrade variables, for clarity.|
|Previous:||From: Robert Haas||Date: 2011-01-05 20:06:31|
|Subject: Re: Re: [COMMITTERS] pgsql: Reduce spurious Hot Standby
conflicts from never-visible records|