Re: [HACKERS] Multiple synchronous_standby_names rules

[Michael Paquier]

On Thu, Jan 12, 2017 at 9:53 AM, James Sewell  wrote:
> What is needed to support this is the ability to configure Px with something 
> like:
>
>  1 (P1, P2, P3), 1 (D1, D2, D3)
>
> Would there be any appetite for this - or would it be seen as over 
> complication of the current rules?

There have been discussions about being able to do that and there are
really use cases where that would be useful. As lately quorum commit
has been committed, we have a better idea of the grammar to use
(yeah!), though there are a couple of things remaining regarding the
design of node subsets:
- How to define group names? Making them mandatory would likely be the
way to go.
- How to represent that intuitively in pg_stat_replication? Perhaps
the answer here is an extra column in this system view.
-- 
Michael


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[HACKERS] Multiple synchronous_standby_names rules

[James Sewell]

Hello,

When working with a production (P) and a DR (D) environment it is often a
requirement to be able to protect against data loss when promoting within a
site, and also when losing A and promoting a master at D.

The current synchronous_standby_names do not allow this.

In a simple example we could take the following nodes:

P1 (current master), P2, P3
D1, D2, D3

Where P1 is replicating to (P2, P3, D1, D2, D3).

The closest synchronous_standby_names  setting you could get to my use case
would be:

1 (D1, D2, D3)

This would allow the loss of either site without losing data - however it
would not allow promotion within site P from P1 -> (P2 | P3)  without the
potential for data loss.

What is needed to support this is the ability to configure Px with
something like:

 1 (P1, P2, P3), 1 (D1, D2, D3)

Would there be any appetite for this - or would it be seen as over
complication of the current rules?

Cheers,


James Sewell,
PostgreSQL Team Lead / Solutions Architect



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