Re: [Patch] ALTER SYSTEM READ ONLY

On Wed, Jun 17, 2020 at 9:37 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Wed, Jun 17, 2020 at 10:58 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> > Lastly, the arguments in favor seem pretty bogus. HA switchover normally
> > involves just killing the primary server, not expecting that you can
> > leisurely issue some commands to it first.
>
> Yeah, that's exactly the problem I want to fix. If you kill the master
> server, then you have interrupted service, even for read-only queries.
>

Yeah, but if there is a synchronuos_standby (standby that provide sync
replication), user can always route the connections to it
(automatically if there is some middleware which can detect and route
the connection to standby)

> That sucks. Also, even if you don't care about interrupting service on
> the master, it's actually sorta hard to guarantee a clean switchover.
>

Fair enough. However, it is not described in the initial email
(unless I have missed it; there is a mention that this patch is one
part of that bigger feature but no further explanation of that bigger
feature) how this feature will allow a clean switchover. I think
before we put the system into READ ONLY state, there could be some WAL
which we haven't sent to standby, what we do we do for that.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com