Re: [patch] demote

On 2020/06/19 0:22, Robert Haas wrote:
> On Thu, Jun 18, 2020 at 8:41 AM Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
>> ISTM that a clean switchover is possible without "ALTER SYSTEM READ ONLY".
>> What about the following procedure?
>>
>> 1. Demote the primary to a standby. Then this demoted standby is read-only.
>> 2. The orignal standby automatically establishes the cascading replication
>> connection with the demoted standby.
>> 3. Wait for all the WAL records available in the demoted standby to be streamed
>> to the orignal standby.
>> 4. Promote the original standby to new primary.
>> 5. Change primary_conninfo in the demoted standby so that it establishes
>> the replication connection with new primary.
>>
>> So it seems enough to implement "demote" feature for a clean switchover.
>
> There's something to that idea. I think it somewhat depends on how
> invasive the various operations are. For example, I'm not really sure
> how feasible it is to demote without a full server restart that kicks
> out all sessions. If that is required, it's a significant disadvantage
> compared to ASRO.

Even with ASRO, the server restart is necessary and RO sessions are
kicked out when demoting RO primary to a standby, i.e., during a clean
switchover?

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION