Re: Issues in Replication Progress Tracking

On 2015-05-21 09:40:58 +0530, Amit Kapila wrote:
> On Thu, May 21, 2015 at 12:42 AM, Andres Freund <andres@anarazel.de> wrote:
> >
> > On 2015-05-20 19:27:05 +0530, Amit Kapila wrote:
> >
> > > 13.
> > > In function replorigin_session_setup() and or
> > > replorigin_session_advance(), don't we need to WAL log the
> > > use of Replication state?
> >
> > No, the point is that the replication progress is persisted via an extra
> > data block in the commit record. That's important for both performance
> > and correctness, because otherwise it gets hard to tie a transaction
> > made during replay with the update to the progress. Unless you use 2PC
> > which isn't really an alternative.
> >
> 
> Okay, but what triggered this question was the difference of those functions
> as compare to when user call function pg_replication_origin_advance().
> pg_replication_origin_advance() will WAL log the information during that
> function call itself (via replorigin_advance()).  So even if the transaction
> issuing pg_replication_origin_advance() function will abort, it will still
> update
> the Replication State, why so?

I don't see a problem here. pg_replication_origin_advance() is for
setting up the initial position/update the position upon configuration
changes. It'd be a fair amount of infrastructure to make it tie into
transactions - without a point to it afaics?

(Just to be clear, I plan to address all the points I've not commented
upon)

Greetings,

Andres Freund