Re: Exposing the Xact commit order to the user

Jan Wieck wrote:
> >> Reading the entire WAL just to find all COMMIT records, then go back to 
> >> the origin database to get the actual replication log you're looking for 
> >> is simpler and more efficient? I don't think so.
> > 
> > Agreed, but I think I've not explained myself well enough.
> > 
> > I proposed two completely separate ideas; the first one was this:
> > 
> > If you must get commit order, get it from WAL on *origin*, using exact
> > same code that current WALSender provides, plus some logic to read
> > through the WAL records and extract commit/aborts. That seems much
> > simpler than the proposal you outlined and as SR shows, its low latency
> > as well since commits write to WAL. No need to generate event ticks
> > either, just use XLogRecPtrs as WALSender already does.
> > 
> > I see no problem with integrating that into core, technically or
> > philosophically.
> > 
> 
> Which means that if I want to allow a consumer of that commit order data 
> to go offline for three days or so to replicate the 5 requested, low 
> volume tables, the origin needs to hang on to the entire WAL log from 
> all 100 other high volume tables?

I suggest writing an external tool that strips out what you need that
can be run at any time, rather than creating a new data format and
overhead for this usecase.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com