Re: Copy function for logical replication slots

On 28 June 2018 at 10:51, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:

> Hi,
>
> I'd like to propose a copy function for logical replication slots.
> Currently when we create a new logical replication slot it starts to
> read WAL from an LSN of the current insert. This function copies a
> existing logical replication slot while changing output plugin and
> persistence. That is, the copied new replication slot starts from the
> same LSN as the source one. Since a new copied slot starts from the
> same LSN of existing one we don't need to care about WAL reservation.
>

Strong agreement from me.

The inability to switch plugins is a massive pain. I've worked around it
with similar functions bundled into the extensions I work with that do
logical decoding related work. It makes sense to have it in core.

A use case I imagined is for investigations for example. I mean that
> when replication collision occurs on subscriber there is no way to see
> what replicated data is conflicting (perhaps error log helps it but is
> not detailed) and there is no way to advance a replication origin in
> order to exactly skip to apply conflicting data.

pglogical handles this by letting you peek the slot in a separate json
protocol output mode, but that doesn't help with pgoutput.

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