Re: Exposing the Xact commit order to the user

On 6/1/2010 11:09 AM, Bruce Momjian wrote:
> Jan Wieck wrote:
>> >> > 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.
>> > 
>> 
>> Stripping it out from what?
> 
> Stripping it from the WAL.  Your system seems to require double-writes
> on a commit, which is something we have avoided in the past.
> 

Your suggestion seems is based on several false assumptions. This does 
neither require additional physical writes on commit, nor is consuming 
the entire WAL just to filter out commit records anything even remotely 
desirable for systems like Londiste or Slony.


Jan

-- 
Anyone who trades liberty for security deserves neither
liberty nor security. -- Benjamin Franklin