Re: Re: [COMMITTERS] pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

On Fri, May 27, 2016 at 9:58 AM, Kevin Grittner <kgrittn@gmail.com> wrote:
> On Tue, May 24, 2016 at 4:56 PM, Andres Freund <andres@anarazel.de> wrote:

>> If an old session with >= repeatable read accesses a clustered
>> table (after the cluster committed), they'll now not see any
>> errors, because all the LSNs look new.
>
> Again, it is new LSNs that trigger errors; if the page has not been
> written recently the LSN is old and there is no error.  I think you
> may be seeing problems based on getting the basics of this
> backwards.

I am reviewing the suggestion of a possible bug now, and will make
it my top priority until resolved.  By the end of 1 June I will
either have committed a fix or posted an explanation of why the
concern is mistaken, with test results to demonstrate correct
behavior.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company