On 13 June 2013 02:18, Stephen Frost <sfrost@snowman.net> wrote:
> * Ants Aasma (ants@cybertec.at) wrote:
>> In a cluster setting you take the CSN value on the master, then before
>> starting execution on a standby you wait until that the standby has
>> replayed enough WAL to reach the CSN point read from the master and
>> you know that after that everything that the snapshot can see is also
>> replayed on the standby.
>
> This does make a lot of sense- but to clarify, this would only be for
> certain isolation levels, right? Or would we implement this for every
> snapshot taken in a read-committed transaction?
That idea is not dependent upon CSNs.
It is an option for us to implement snapshot synchronisation now, we
just haven't done it yet.
I'm currently working on exporting/importing snapshots on standbys,
which is a precursor to that idea.
None of the above is any easier/harder with CSNs, nor would it
delay/accelerate delivery of such features.
--Simon Riggs http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services