Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> Make a hard state change from catchup to streaming mode.
>> More useful state change for monitoring purposes, plus a
>> required change for synchronous replication patch.
>
> As far as I can see, this patch was not posted or discussed before
> commit, and I'm not sure it's the behavior everyone wants. It has
> the effect of preventing the system from ever going backwards from
> "streaming" to "catchup". Is that what we want?
We are looking at moving to streaming replication instead of WAL
file shipping, but we often have WAN outages. These can last
minutes, hours, or even a few days. What would be the impact of
this patch on us during and after such outages?
I don't know how well such experience generalizes, but my personal
experience with replication technology is that "hard state changes"
tend to make things more "clunky" and introduce odd issues at the
state transitions. Where different message types are intermingled
without such hard state changes, I've seen more graceful behavior.
Of course, take that with a grain of salt -- I haven't read the
patch and am talking in generalities based on having written a
couple serious replication tools in the past, and having used a few
others.
-Kevin