Re: Standalone synchronous master

On Sat, Jan 11, 2014 at 01:29:23PM +0530, Amit Kapila wrote:
> Okay, this is one way of providing this new mode, others could be:
> 
> a.
> Have just one GUC sync_standalone_mode = true|false and make
> this as PGC_POSTMASTER parameter, so that user is only
> allowed to set this mode at startup. Even if we don't want it as
> Postmaster parameter, we can mention to users that they can
> change this parameter only before server reaches current situation.
> I understand that without any alarm or some other way, it is difficult
> for user to know and change it, but I think in that case he should
> set it before server startup.
> 
> b.
> On above lines, instead of boolean parameter, provide a parameter
> similar to current one such as available_synchronous_standby_names,
> setting of this should follow what I said in point a. The benefit in this
> as compare to 'a' is that it appears to be more like what we currently have.
> 
> I think if we try to solve this problem by providing a way so that user
> can change it at runtime or when the problem actually occurred, it can
> make the UI more complex and difficult for us to provide a way so that
> user can be alerted on such situation. We can keep our options open
> so that if tomorrow, we can find any reasonable way, then we can
> provide it to user a mechanism for changing this at runtime, but I don't
> think it is stopping us from providing a way with which user can get the
> benefit of this mode by providing start time parameter.

I am not sure how this would work.  Right now we wait for one of the
synchronous_standby_names servers to verify the writes.   We need some
way of telling the system how long to wait before continuing in degraded
mode.  Without a timeout and admin notification, it doesn't seem much
better than our async mode, which is what many people were complaining
about.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + Everyone has their own god. +