Re: Support for N synchronous standby servers - take 2

On Fri, May 15, 2015 at 8:55 PM, Beena Emerson <memissemerson(at)gmail(dot)com> wrote:
> There was a discussion on support for N synchronous standby servers started
> by Michael. Refer
> http://archives.postgresql.org/message-id/CAB7nPqR9c84ig0ZUvhMQAMq53VQsD4rC82vYci4Dr27PVOFf9w@mail.gmail.com
> . The use of hooks and dedicated language was suggested, however, it seemed
> to be an overkill for the scenario and there was no consensus on this.
> Exploring GUC-land was preferred.

Cool.

> Please find attached a patch, built on Michael's patch from above mentioned
> thread, which supports choosing different number of nodes from each set i.e.
> k nodes from set 1, l nodes from set 2, so on.
> The format of synchronous_standby_names has been updated to standby name
> followed by the required count separated by hyphen. Ex: 'aa-1, bb-3'. The
> transaction waits for all the specified number of standby in each group. Any
> extra nodes with the same name will be considered potential. The special
> entry * for the standby name is also supported.

I don't think that this is going in the good direction, what was
suggested mainly by Robert was to use a micro-language that would
allow far more extensibility that what you are proposing. See for
example CA+TgmobPWoeNMMEpfx0jWRvQufxVbqRv26Ezq_XHk21GxrXo9w(at)mail(dot)gmail(dot)com
for some ideas. IMO, before writing any patch in this area we should
find a clear consensus on what we want to do. Also, unrelated to this
patch, we should really get first the patch implementing the... Hum...
infrastructure for regression tests regarding replication and
archiving to be able to have actual tests for this feature (working on
it for next CF).

+ if (!SplitIdentifierString(standby_detail, '-', &elemlist2))
+ {
+ /* syntax error in list */
+ pfree(rawstring);
+ list_free(elemlist1);
+ return 0;
+ }
At quick glance, this looks problematic to me if application_name has an hyphen.

Regards,
--
Michael