Re: The way to know whether the standby has caught up with the master

On Wed, May 25, 2011 at 12:28 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
> On Wed, May 25, 2011 at 2:16 PM, Heikki Linnakangas
>>>
>>> To achieve that, I'm thinking to change walsender so that, when the
>>> standby
>>> has caught up with the master, it sends back the message indicating that
>>> to
>>> the standby. And I'm thinking to add new function (or view like
>>> pg_stat_replication)
>>> available on the standby, which shows that info.
>>
>> By the time the standby has received that message, it might not be caught-up
>> anymore because new WAL might've been generated in the master already.
>
> Right. But, thanks to sync rep, until such a new WAL has been replicated to
> the standby, the commit of transaction is not visible to the client. So, even if
> there are some WAL not replicated to the standby, the clusterware can promote
> the standby safely without any data loss (to the client point of view), I think.
>

then, you also need to transmit to the standby if it is the current
sync standby.

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