Re: Standbys, txid_current_snapshot, wraparound

On Thu, Mar 29, 2012 at 3:04 PM, Marko Kreen <markokr(at)gmail(dot)com> wrote:
> On Thu, Mar 29, 2012 at 02:46:23PM +0100, Simon Riggs wrote:
>> On Thu, Mar 29, 2012 at 12:06 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> > Patch coming in a few hours.
>>
>> This is more straightforward than I was thinking. We just need to
>> initialise XLogCtl at the right place.
>
> Looks good to me.  That should fix the problem with standbys then.
>
>
> Next question: how can flipping archive_mode on and off,
> with restarts, near wraparound point, break epoch on master?
>
>  http://lists.pgfoundry.org/pipermail/skytools-users/2012-March/001609.html
>
> Any ideas?
>
> Could WAL playback from backend with different archive_mode setting
> cause it somehow?

The current code would allow it, if you managed to go for 4 billion
xids between checkpoints. If that happened, it would give an off by
one error each time it happened.

I don't believe that is possible.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services