Re: Initial load from standby in logical replication.

On Thu, Jan 31, 2019 at 4:09 PM Achilleas Mantzios <
achill(at)matrix(dot)gatewaynet(dot)com> wrote:

> On 31/1/19 3:55 μ.μ., Radoslav Nedyalkov wrote:
> > Hi All,
> > We want to setup a logical replica with initial load from physical
> standby. (all pg10.5)
> > Basically what we tested is:
> > 1.on the master: create publication and logical slot.
> > 2.on the standby: pause the stanby. (lsn from 1. is already replayed).
> > 3.on the standby: get last replayed lsn, pg_last_wal_replay_lsn().
> > 4.export/import the data into the logical replica.
> > 5.on the logical replica: create subscription
> with pg_replication_origin_advance'd to the lsn from 3.
> > 6.on the logical replica: enable subscription.
> >
> > On a test setup with some bulk inserts results are encouraging.
> > Still we're not that confident. Does the procedure looks okay?
> > What if standby is paused at COMMIT lsn?
> Who is gonna consume data from the primary's replication slot? If there is
> no subscriber connected and reading data, then the primary will think that
> the subscriber is down and will accumulate WALs
> till some replication client is connected to it (which will not happen
> since the subscriber points to the standby).
>
Yes. that's clear. Primary will accumulate WALs until logical replica
connects to it.
The point is to offload the primary from massive initial copying.

> > Thanks!
> > Radoslav Nedyalkov
> >
> --
> Achilleas Mantzios
> IT DEV Lead
> IT DEPT
> Dynacom Tankers Mgmt
>
>
>