Re: PostgreSQL replication failover

On Wed, 2021-01-13 at 09:27 +0100, Jan Peters wrote:
> we are running postgresqlserver on s390 zLinux machines. The distribution
> is RedHat 7 and RedHat 8, so we do not have the many x86 tools available.
>
> We always run 2 instances with a replication (streaming) async mode, the replica
> is in hot_standby and we use it for read-only accesses. About the setup we have the following question:
>
> How is an orderly failover accomplished? Our current procedure is.
>
> 1. primary stop
> 2. promote replica to primary
> 3. create standby.signal on old primary
> 4. change primary_conninfo on old primary
> 5. start old primary as new replica
>
> Is this processing correct? Are there any other steps that simplify a failover?
> How can we be sure that all changes have been transferred from the old master to the replica?

What you describe is not a failover, but a switchover.

If you shut down the primary server cleanly, all changes will be replicated,
so you should be good.

During a failover, that is, if the primary suddenly fails, there is always
the possibility that you lose some transactions, unless you use synchronous
replication.

Yours,
Laurenz Albe
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