Re: Suggestions on message transfer among backends

On Tue, Mar 12, 2019 at 1:59 PM Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>
wrote:

> On 11/03/2019 18:36, Andy Fan wrote:
> > Hi:
> > I need some function which requires some message exchange among
> > different back-ends （connections).
> > specially I need a shared hash map and a message queue.
> >
> > Message queue: it should be many writers, 1 reader. Looks POSIX
> > message queue should be OK, but postgre doesn't use it. is there any
> > equivalent in PG?
> >
> > shared hash map: the number of items can be fixed and the value can be
> > fixed as well.
> >
> > any keywords or explanation will be extremely helpful.
> You may use shm_mq (shared memory queue) and hash tables (dynahash.c) in
> shared memory (see ShmemInitHash() + shmem_startup_hook)
> >
> > Thanks
>
> --
> Andrey Lepikhov
> Postgres Professional
> https://postgrespro.com
> The Russian Postgres Company
>

Thanks Andrey and all people replied this! dynahash/ShmemInitHash is the
one I'm using and it is ok for my purposes.
I planned to use posix/system v message queue, since they are able to
support multi readers/multi writer.
I just don't know why shm_mq is designed to single-reader & single-writer.