Re: Re: [COMMITTERS] pgsql: Make a hard state change from catchup to streaming mode.
От | Simon Riggs |
---|---|
Тема | Re: Re: [COMMITTERS] pgsql: Make a hard state change from catchup to streaming mode. |
Дата | |
Msg-id | 1298076135.2226.6108.camel@ebony обсуждение исходный текст |
Ответ на | Re: [COMMITTERS] pgsql: Make a hard state change from catchup to streaming mode. ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>) |
Список | pgsql-hackers |
On Fri, 2011-02-18 at 09:41 -0600, Kevin Grittner wrote: > Robert Haas <robertmhaas@gmail.com> wrote: > > Simon Riggs <simon@2ndquadrant.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? None at all. The patch introduces no behavioural changes, only a useful, but minor re-categorisation of what is already happening so that its easier to monitor what happens following startup of a standby. > 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. I respect your experience. -- Simon Riggs http://www.2ndQuadrant.com/books/PostgreSQL Development, 24x7 Support, Training and Services
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