Re: bogus: logical replication rows/cols combinations

On Mon, May 2, 2022 at 6:11 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
>
> On 2022-May-02, Amit Kapila wrote:
>
>
> > I think it is possible to expose a list of publications for each
> > walsender as it is stored in each walsenders
> > LogicalDecodingContext->output_plugin_private. AFAIK, each walsender
> > can have one such LogicalDecodingContext and we can probably share it
> > via shared memory?
>
> I guess we need to create a DSM each time a walsender opens a
> connection, at START_REPLICATION time. Then ALTER PUBLICATION needs to
> connect to all DSMs of all running walsenders and see if they are
> reading from it. Is that what you have in mind? Alternatively, we
> could have one DSM per publication with a PID array of all walsenders
> that are sending it (each walsender needs to add its PID as it starts).
> The latter might be better.
>

While thinking about using DSM here, I came across one of your commits
f2f9fcb303 which seems to indicate that it is not a good idea to rely
on it but I think you have changed dynamic shared memory to fixed
shared memory usage because that was more suitable rather than DSM is
not portable. Because I see a commit bcbd940806 where we have removed
the 'none' option of dynamic_shared_memory_type. So, I think it should
be okay to use DSM in this context. What do you think?

--
With Regards,
Amit Kapila.