Re: Standalone synchronous master
От | Bruce Momjian |
---|---|
Тема | Re: Standalone synchronous master |
Дата | |
Msg-id | 20140110154725.GD4873@momjian.us обсуждение исходный текст |
Ответ на | Re: Standalone synchronous master (Amit Kapila <amit.kapila16@gmail.com>) |
Ответы |
Re: Standalone synchronous master
(Simon Riggs <simon@2ndQuadrant.com>)
Re: Standalone synchronous master ("Joshua D. Drake" <jd@commandprompt.com>) Re: Standalone synchronous master (Amit Kapila <amit.kapila16@gmail.com>) |
Список | pgsql-hackers |
On Fri, Jan 10, 2014 at 10:21:42AM +0530, Amit Kapila wrote: > On Thu, Jan 9, 2014 at 10:45 PM, Bruce Momjian <bruce@momjian.us> wrote: > > > > I think RAID-1 is a very good comparison because it is successful > > technology and has similar issues. > > > > RAID-1 is like Postgres synchronous_standby_names mode in the sense that > > the RAID-1 controller will not return success until writes have happened > > on both mirrors, but it is unlike synchronous_standby_names in that it > > will degrade and continue writes even when it can't write to both > > mirrors. What is being discussed is to allow the RAID-1 behavior in > > Postgres. > > > > One issue that came up in discussions is the insufficiency of writing a > > degrade notice in a server log file because the log file isn't durable > > from server failures, meaning you don't know if a fail-over to the slave > > lost commits. The degrade message has to be stored durably against a > > server failure, e.g. on a pager, probably using a command like we do for > > archive_command, and has to return success before the server continues > > in degrade mode. I assume degraded RAID-1 controllers inform > > administrators in the same way. > > Here I think if user is aware from beginning that this is the behaviour, > then may be the importance of message is not very high. > What I want to say is that if we provide a UI in such a way that user > decides during setup of server the behavior that is required by him. > > For example, if we provide a new parameter > available_synchronous_standby_names along with current parameter > and ask user to use this new parameter, if he wishes to synchronously > commit transactions on another server when it is available, else it will > operate as a standalone sync master. I know there was a desire to remove this TODO item, but I think we have brought up enough new issues that we can keep it to see if we can come up with a solution. I have added a link to this discussion on the TODO item. I think we will need at least four new GUC variables: * timeout control for degraded mode * command to run during switch to degraded mode * command to run during switch from degraded mode * read-only variable to report degraded mode -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. +
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