Re: snapshot too old, configured by time

On Sat, Apr 23, 2016 at 10:20:19AM -0400, Bruce Momjian wrote:
> On Sat, Apr 23, 2016 at 12:48:08PM +0530, Amit Kapila wrote:
> > On Sat, Apr 23, 2016 at 8:34 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > >
> > > I kind of agreed with Tom about just aborting transactions that held
> > > snapshots for too long, and liked the idea this could be set per
> > > session, but the idea that we abort only if a backend actually touches
> > > the old data is very nice.  I can see why the patch author worked hard
> > > to do that.

As I understand it, a transaction trying to access a shared buffer
aborts if there was a cleanup on the page that removed rows it might be
interested in. How does this handle cases where vacuum removes _pages_
from the table? Does vacuum avoid this when there are running
transactions?

> Also, it seems we have similar behavior already in applying WAL on the
> standby --- we delay WAL replay when there is a long-running
> transaction. Once the time expires, we apply the WAL. Do we cancel the
> long-running transaction at that time, or wait for the long-running
> transaction to touch some WAL we just applied? If the former, does
> Kevin's new code allow us to do the later?

Is this a TODO item?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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