Re: Avoid full page images in streaming replication?

On Oct 22, 2015 23:38, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> writes:
> > ISTM it should be possible to avoid sending full page writes to a
> > streaming replica once the replica has reached a consistent state. I
> > assume that the replica would still need to write full pages to it's
> > disk in case of a crash, but the sender could insert special WAL records
> > to tell it when to do so, instead of sending the full page image.
> > Presumably this would be a big win for replication over a WAN.
>
> How are you going to make that work without LSNs in the WAL received by
> the replica diverging from those in the master's WAL?
>

We could in theory send a "this would be been a fpi but it's skipped"
record which would only exist in streaming and just make the standby write
a noop of some kind? It would still be on the standby but it would at least
not consume the bandwidth. Just skip sending the actual contents of the
fpi.

/Magnus