Re: sync rep design architecture (was "disposition of remaining patches")

On Fri, Feb 25, 2011 at 8:40 AM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> I didn't get the Streaming Rep + Hot Standby features I wanted in 9.0 either.  But committing what was reasonable to include in that version let me march forward with very useful new code, doing another year of development on my own projects and getting some new things get fixed in core.  And so far it looks like 9.1 will sort out all of the kinks I was unhappy about.  The same sort of thing will need to happen to get Sync Rep committed and then appropriate for more use cases.  There isn't any margin left for discussions of scope creep left here; really it's "is this subset useful for some situations and stable enough to commit" now.

I mostly wanted to raise the issue to not be a blocker, but an attempt
to avoid boxing ourselves in for growing such a feature in 9.2. if
9.1 ships with the syncrep patch as-conceived, it'll just mean that
it'll be hard/not possible to offer syncrep to users as well as at the
"infrastructure service provider" level...which is, actually, quite
fine -- most current users likely don't want to take the performance
hit of syncrep all the time, but to live with it during a switchover
is quite fine. I just wanted to make a reasonable effort to ensure
its possibility in a 9.2-like timeframe.

>> 2. The unprivileged user can disable syncrep, in any situation. This
>> flexibility is *great*, but you don't really want people to do it when
>> one is performing the switchover.
>
> For the moment you may have to live with a situation where user connections must be blocked during the brief moment of switchover to eliminate this issue.  That's what I end up doing with 9.0 production systems to get a really clean switchover, there's a second of hiccup even in the best case.  I'm not sure yet of the best way yet to build a UI to make that more transparent in the sync rep case.  It's sure not a problem that's going to get solved in this release though.

I'm totally okay killing all backends during the switchover between
9.1 and 9.2 releases, unless I get super clever with pgbouncer...which
I will have to do anyway.

--
fdr