Обсуждение: [GENERAL] Lag in asynchronous replication

On Thu, Mar 23, 2017 at 11:37 PM, Subhankar Chattopadhyay
<subho.atg@gmail.com> wrote:
> in case of automated failover i want to check if slave is lagging from
> master and only if it is in sync, i want to do failover. But I am working in
> a virtual cloud environment so by that time the master VM may not be
> available to me. How can i check the lag in that case ?

Is your environment switching dynamically to async if the lag is too
important? If not, once you have reached a sync state, the master
would wait for all transactions commits to complete on the slave, so
once the client has received a commit confirmation you have the
guarantee that the data is already flushed on the slave. In this case
you don't need to know what happens on the master.
--
Michael

On Fri, Mar 24, 2017 at 3:11 PM, Subhankar Chattopadhyay
<subho.atg@gmail.com> wrote:
> Are you asking to have slave with synchronous replication?

(top-posting is annoying)

No, slaves cannot do synchronous replication. I am just telling that
once you are sure that a sync state has been achieved on the master,
you have the guarantee that data gets synchronously replicated on the
standbys as long as you do *not* change synchronous_standby_names. So
there is no actual need to know what's the state of the master during
a failover to a sync standby.
--
Michael